Core Java Questions with Answers

CORE JAVA

Question: What is a compilation unit?
Answer: A compilation unit is a Java source code file.

Question: What restrictions are placed on method overriding?
Answer:: Overridden methods must have the same name, argument list, and return type.
The overriding method may not limit the access of the method it overrides.
The overriding method may not throw any exceptions that may not be thrown by the overridden method.

Question: How can a dead thread be restarted?
Answer: A dead thread cannot be restarted.

Question: What happens if an exception is not caught?
Answer: An uncaught exception results in the uncaughtException() method of the thread's ThreadGroup being invoked, which eventually results in the termination of the program in which it is thrown.

Question: Which arithmetic operations can result in the throwing of an ArithmeticException?
Answer: Integer / and % can result in the throwing of an ArithmeticException

Question: Can an abstract class be final?
Answer: An abstract class may not be declared as final

Question: What happens if a try-catch-finally statement does not have a catch clause to handle an exception that is thrown within the body of the try statement?
Answer: The exception propagates up to the next higher level try-catch statement (if any) or results in the program's termination

Question: What is numeric promotion?
Answer: Numeric promotion is the conversion of a smaller numeric type to a larger numeric type, so that integer and floating-point operations may take place. In numerical promotion, byte, char, and short values are converted to int values. The int values are also converted to long values, if necessary. The long and float values are converted to double values, as required

Question: What is the difference between a public and a non-public class?
Answer: A public class may be accessed outside of its package. A non-public class may not be accessed outside of its package.

Question: To what value is a variable of the boolean type automatically initialized?
Answer: The default value of the boolean type is false

Question: Can try statements be nested?
Answer: Yes

Question: What is the difference between the prefix and postfix forms of the ++ operator?
Answer: The prefix form performs the increment operation and returns the value of the increment operation. The postfix form returns the current value all of the expression and then performs the increment operation on that value.

Question: What is the purpose of a statement block?
Answer: A statement block is used to organize a sequence of statements as a single statement group

Question: What is a Java package and how is it used?
Answer: A Java package is a naming context for classes and interfaces. A package is used to create a separate name space for groups of classes and interfaces. Packages are also used to organize related classes and interfaces into a single API unit and to control accessibility to these classes and interfaces.

Question: What modifiers may be used with a top-level class?
Answer: A top-level class may be public, abstract, or final.

Question: What are the Object and Class classes used for?
Answer: The Object class is the highest-level class in the Java class hierarchy. The Class class is used to represent the classes and interfaces that are loaded by a Java program.

Question: How does a try statement determine which catch clause should be used to handle an exception?
Answer: When an exception is thrown within the body of a try statement, the catch clauses of the try statement are examined in the order in which they appear. The first catch clause that is capable of handling the exception is executed. The remaining catch clauses are ignored.

Question: What are synchronized methods and synchronized statements?
Answer: Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement.

Question: What is the difference between an if statement and a switch statement?
Answer: The if statement is used to select among two alternatives. It uses a boolean expression to decide which alternative should be executed. The switch statement is used to select among multiple alternatives. It uses an int expression to determine which alternative should be executed.

Question: What is the diffrence between inner class and nested class?
Answer: When a class is defined within a scope od another class, then it becomes inner class.
If the access modifier of the inner class is static, then it becomes nested class.

Question: Diffrence between JRE And JVM AND JDK
Answer: The "JDK" is the Java Development Kit. I.e., the JDK is bundle of software that you can use to develop Java based software. The "JRE" is the Java Runtime Environment. I.e., the JRE is an implementation of the Java Virtual Machine which actually executes Java programs. Typically, each JDK contains one (or more) JRE's along with the various development tools like the Java source compilers, bundling and deployment tools, debuggers, development libraries, etc.

Question: Why is not recommended to have instance variables in Interface
Answer: By Default, All data members and methods in an Interface are public. Having public variables in a class that will be implementing it will be violation of the Encapsulation principal. I hope that's pretty ok.. If anybody has a better framed answer. U r welcome at reema_gupta@intersolutions.stpn.soft.net

Question: Can there be an abstract class with no abstract methods in it?
Answer: Yes

Question: Can an Interface be final?
Answer: No

Question: Can an Interface have an inner class?
Answer: Yes public interface abc { static int i=0; void dd(); class a1 { a1() { int j; System.out.println("in interfia"); }; public static void main(String a1[]) { System.out.println("in interfia"); } } }

Question: Can we define private and protected modifiers for variables in interfaces?
Answer: No

Question: What are some alternatives to inheritance?
Answer: Delegation is an alternative to inheritance. Delegation means that you include an instance of another class as an instance variable, and forward messages to the instance. It is often safer than inheritance because it forces you to think about each message you forward, because the instance is of a known class, rather than a new class, and because it doesn't force you to accept all the methods of the super class: you can provide only the methods that really make sense. On the other hand, it makes you write more code, and it is harder to re-use (because it is not a subclass).

Question: Why isn't there operator overloading?
Answer: Because C++ has proven by example that operator overloading makes code almost impossible to maintain. In fact there very nearly wasn't even method overloading in Java, but it was thought that this was too useful for some very basic methods like print(). Note that some of the classes like DataOutputStream have unoverloaded methods like writeInt() and writeByte().

Question: What does it mean that a method or field is "static"?
Answer: Static variables and methods are instantiated only once per class. In other words they are class variables, not instance variables. If you change the value of a static variable in a particular object, the value of that variable changes for all instances of that class.
Static methods can be referenced with the name of the class rather than the name of a particular object of the class (though that works too). That's how library methods like System.out.println() work. out is a static field in the java.lang.System class.

Question: How do I convert a numeric IP address like 192.18.97.39 into a hostname like java.sun.com? (Networking)

Answer: String hostname = InetAddress.getByName("192.18.97.39").getHostName();

Question: Diffrence between JRE And JVM AND JDK
Answer: Java Runtime Environment is used to excute through browser. JVM is used to execute class file.

Question: Why do threads block on I/O?
Answer: Threads block on i/o (that is enters the waiting state) so that other threads may execute while the i/o Operation is performed.

Question: What is synchronization and why is it important?
Answer: With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object's value. This often leads to significant errors.

Question: Is null a keyword?
Answer: The null value is not a keyword.

Question: Which characters may be used as the second character of an identifier,but not as the first character of an identifier?
Answer: The digits 0 through 9 may not be used as the first character of an identifier but they may be used after the first character of an identifier.

Question: What modifiers may be used with an inner class that is a member of an outer class?
Answer: A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.

Question: How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?
Answer: Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.

Question: What are wrapped classes?
Answer: Wrapped classes are classes that allow primitive types to be accessed as objects.

Question: What restrictions are placed on the location of a package statement within a source code file?
Answer: A package statement must appear as the first line in a source code file (excluding blank lines and comments).

Question: What is the difference between preemptive scheduling and time slicing?
Answer: Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.

Question: What is a native method?
Answer: A native method is a method that is implemented in a language other than Java.

Question: What are order of precedence and associativity, and how are they used?
Answer: Order of precedence determines the order in which operators are evaluated in expressions. Associatity determines whether an expression is evaluated left-to-right or right-to-left

Question: What is the catch or declare rule for method declarations?
Answer: If a checked exception may be thrown within the body of a method, the method must either catch the exception or declare it in its throws clause.
Question: Can an anonymous class be declared as implementing an interface and extending a class?

Answer: An anonymous class may implement an interface or extend a superclass, but may not be declared to do both.

Question: What is the range of the char type?
Answer: The range of the char type is 0 to 2^16 - 1.

Question: What is the purpose of finalization?
Answer: The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected.

Question: What is the difference between the Boolean & operator and the && operator?
Answer: If an expression involving the Boolean & operator is evaluated, both operands are evaluated. Then the & operator is applied to the operand. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. The && operator is then applied to the first and second operands. If the first operand evaluates to false, the evaluation of the second operand is skipped.

Question: How many times may an object's finalize() method be invoked by the garbage collector?
Answer: An object's finalize() method may only be invoked once by the garbage collector.

Question: What is the purpose of the finally clause of a try-catch-finally statement?
Answer: The finally clause is used to provide the capability to execute code no matter whether or not an exception is thrown or caught.

Question: What is the argument type of a program's main() method?
Answer: A program's main() method takes an argument of the String[] type.

Question: Which Java operator is right associative?
Answer: The = operator is right associative.

Question: Can a double value be cast to a byte?
Answer: Yes, a double value can be cast to a byte.

Question: What is the difference between a break statement and a continue statement?
Answer: A break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement.

Question: What must a class do to implement an interface?
Answer: It must provide all of the methods in the interface and identify the interface in its implements clause.

Question: What is the advantage of the event-delegation model over the earlier event-inheritance model?
Answer: The event-delegation model has two advantages over the event-inheritance model. First, it enables event handling to be handled by objects other than the ones that generate the events (or their containers). This allows a clean separation between a component's design and its use. The other advantage of the event-delegation model is that it performs much better in applications where many events are generated. This performance improvement is due to the fact that the event-delegation model does not have to repeatedly process unhandled events, as is the case of the event-inheritance model.

Question: How are commas used in the intialization and iteration parts of a for statement?
Answer: Commas are used to separate multiple statements within the initialization and iteration parts of a for statement.

Question: What is an abstract method?
Answer: An abstract method is a method whose implementation is deferred to a subclass.

Question: What value does read() return when it has reached the end of a file?
Answer: The read() method returns -1 when it has reached the end of a file.

Question: Can a Byte object be cast to a double value?
Answer: No, an object cannot be cast to a primitive value.

Question: What is the difference between a static and a non-static inner class?
Answer: A non-static inner class may have object instances that are associated with instances of the class's outer class. A static inner class does not have any object instances.

Question: If a variable is declared as private, where may the variable be accessed?
Answer: A private variable may only be accessed within the class in which it is declared.

Question: What is an object's lock and which object's have locks?
Answer: An object's lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. A thread may execute a synchronized method of an object only after it has acquired the object's lock. All objects and classes have locks. A class's lock is acquired on the class's Class object.

Question: What is the % operator?
Answer: It is referred to as the modulo or remainder operator. It returns the remainder of dividing the first operand by the second operand.

Question: When can an object reference be cast to an interface reference?
Answer: An object reference be cast to an interface reference when the object implements the referenced interface.

Question: Which class is extended by all other classes?
Answer: The Object class is extended by all other classes.

Question: Can an object be garbage collected while it is still reachable?
Answer: A reachable object cannot be garbage collected. Only unreachable objects may be garbage collected.

Question: Is the ternary operator written x : y ? z or x ? y : z ?
Answer: It is written x ? y : z.

Question: How is rounding performed under integer division?
Answer: The fractional part of the result is truncated. This is known as rounding toward zero.

Question: What is the difference between the Reader/Writer class hierarchy and the InputStream/OutputStream class hierarchy?
Answer: The Reader/Writer class hierarchy is character-oriented, and the InputStream/OutputStream class hierarchy is byte-oriented.

Question: What classes of exceptions may be caught by a catch clause?
Answer: A catch clause can catch any exception that may be assigned to the Throwable type. This includes the Error and Exception types.

Question: If a class is declared without any access modifiers, where may the class be accessed?
Answer: A class that is declared without any access modifiers is said to have package access. This means that the class can only be accessed by other classes and interfaces that are defined within the same package.

Question: Does a class inherit the constructors of its superclass?
Answer: A class does not inherit constructors from any of its superclasses.

Question: What is the purpose of the System class?
Answer: The purpose of the System class is to provide access to system resources.

Question: Name the eight primitive Java types.
Answer: The eight primitive types are byte, char, short, int, long, float, double, and boolean.

Question: Which class should you use to obtain design information about an object?
Answer: The Class class is used to obtain information about an object's design.

Question: can the Kawa or any another J-editor export a .EXE file and to be has an install shield
Answer: I didn't know i need an answer.

Question: What modifiers are allowed for methods in an Interface?
Answer: Only public and abstract modifiers are allowed for methods in interfaces.

Question: What are the different identifier states of a Thread?
Answer: The different identifiers of a Thread are:
R - Running or runnable thread
S - Suspended thread
CW - Thread waiting on a condition variable
MW - Thread waiting on a monitor lock
MS - Thread suspended waiting on a monitor lock

Question: What is Externalizable?
Answer: Externalizable is an Interface that extends Serializable Interface. And sends data into Streams in Compressed Format. It has two methods, writeExternal(ObjectOuput out) and readExternal(ObjectInput in)

Question: I made my class Cloneable but I still get 'Can't access protected method clone. Why?
Answer: Yeah, some of the Java books, in particular "The Java Programming Language", imply that all you have to do in order to have your class support clone() is implement the Cloneable interface. Not so. Perhaps that was the intent at some point, but that's not the way it works currently. As it stands, you have to implement your own public clone() method, even if it doesn't do anything special and just calls super.clone().

Question: What is a local, member and a class variable?
Answer: Variables declared within a method are "local" variables.
Variables declared within the class i.e not within any methods are "member" variables (global variables).
Variables declared within the class i.e not within any methods and are defined as "static" are class variables

Question: What gives java it's "write once and run anywhere" nature?
Answer: Java is compiled to be a byte code which is the intermediate language between source code and machine code. This byte code is not platorm specific and hence can be fed to any platform. After being fed to the JVM, which is specific to a particular operating system, the code platform specific machine code is generated thus making java platform independent.

Question: What are the four corner stones of OOP ?
Answer: Abstraction, Encapsulation, Polymorphism and Inheritance

Question: Difference between a Class and an Object ?
Answer: A class is a definition or prototype whereas an object is an instance or living representation of the prototype

Question: What is the difference between method overriding and overloading?
Answer: Overriding is a method with the same name and arguments as in a parent, whereas overloading is the same method name but different arguments

Question: What is a "stateless" protocol ?
Answer: Without getting into lengthy debates, it is generally accepted that protocols like HTTP are stateless i.e. there is no retention of state between a transaction which is a single request response combination

Question: What is constructor chaining and how is it achieved in Java ?
Answer: A child object constructor always first needs to construct its parent (which in turn calls its parent constructor.). In Java it is done via an implicit call to the no-args constructor as the first statement.

Question: What is passed by ref and what by value ?
Answer: All Java method arguments are passed by value. However, Java does manipulate objects by reference, and all object variables themselves are references

Question: You can create a String object as String str = "abc"; Why cant a button
object be created as Button bt = "abc";? Explain
Answer: The main reason you cannot create a button by Button bt1= "abc"; is because "abc" is a literal string (something slightly different than a String object, by-the-way) and bt1 is a Button object. The only object in Java that can be assigned a literal String is java.lang.String. Important to note that you are NOT calling a java.lang.String constuctor when you type String s = "abc";

Question: What does the "abstract" keyword mean in front of a method? A class?
Answer: Abstract keyword declares either a method or a class. If a method has a abstract keyword in front of it,it is called abstract method.Abstract method hs no body.It has only arguments and return type.Abstract methods act as placeholder methods that are implemented in the subclasses.
Abstract classes can't be instantiated.If a class is declared as abstract,no objects of that class can be created.If a class contains any abstract method it must be declared as abstract

Question: How many methods do u implement if implement the Serializable Interface?
Answer: The Serializable interface is just a "marker" interface, with no methods of its own to implement. Other 'marker' interfaces are
java.rmi.Remote
java.util.EventListener

Question: What are the practical benefits, if any, of importing a specific class rather than an entire package (e.g. import java.net.* versus import java.net.Socket)?
Answer: It makes no difference in the generated class files since only the classes that are actually used are referenced by the generated class file. There is another practical benefit to importing single classes, and this arises when two (or more) packages have classes with the same name. Take java.util.Timer and javax.swing.Timer, for example. If I import java.util.* and javax.swing.* and then try to use "Timer", I get an error while compiling (the class name is ambiguous between both packages). Let's say what you really wanted was the javax.swing.Timer class, and the only classes you plan on using in java.util are Collection and HashMap. In this case, some people will prefer to import java.util.Collection and import java.util.HashMap instead of importing java.util.*. This will now allow them to use Timer, Collection, HashMap, and other javax.swing classes without using fully qualified class names in.


Question: What is the difference between logical data independence and physical data independence?
Answer: Logical Data Independence - meaning immunity of external schemas to changeds in conceptual schema. Physical Data Independence - meaning immunity of conceptual schema to changes in the internal schema.

Question: What is user defined exception ?
Answer: Apart from the exceptions already defined in Java package libraries, user can define his own exception classes by extending Exception class.

Question: Difference Between Abstraction and Encapsulation
Answer: Abstraction is removing some distinctions between objects, so as to show their commonalities.
Encapsulation is hiding the details of the implementation of an object so that there are no external dependencies on the particular implementation.

Question: Why are there no global variables in Java?
Answer: Global variables are considered bad form for a variety of reasons:
· Adding state variables breaks referential transparency (you no longer can understand a statement or expression on its own: you need to understand it in the context of the settings of the global variables).
· State variables lessen the cohesion of a program: you need to know more to understand how something works. A major point of Object-Oriented programming is to break up global state into more easily understood collections of local state.
· When you add one variable, you limit the use of your program to one instance. What you thought was global, someone else might think of as local: they may want to run two copies of your program at once.
For these reasons, Java decided to ban global variables.

Question: What does it mean that a class or member is final?
Answer: A final class can no longer be subclassed. Mostly this is done for security reasons with basic classes like String and Integer. It also allows the compiler to make some optimizations, and makes thread safety a little easier to achieve.
Methods may be declared final as well. This means they may not be overridden in a subclass.
Fields can be declared final, too. However, this has a completely different meaning. A final field cannot be changed after it's initialized, and it must include an initializer statement where it's declared. For example,
public final double c = 2.998;
It's also possible to make a static field final to get the effect of C++'s const statement or some uses of C's #define, e.g.
public static final double c = 2.998;


Question: What does it mean that a method or class is abstract?
Answer: An abstract class cannot be instantiated. Only its subclasses can be instantiated. You indicate that a class is abstract with the abstract keyword like this:
public abstract class Container extends Component {
Abstract classes may contain abstract methods. A method declared abstract is not actually implemented in the current class. It exists only to be overridden in subclasses. It has no body. For example,
public abstract float price();
Abstract methods may only be included in abstract classes. However, an abstract class is not required to have any abstract methods, though most of them do.
Each subclass of an abstract class must override the abstract methods of its superclasses or itself be declared abstract.


Question: what is a transient variable?
Answer: transient variable is a variable that may not be serialized.

Question: How are Observer and Observable used?
Answer: Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.

Question: Can a lock be acquired on a class?
Answer: Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.

Question: What state does a thread enter when it terminates its processing?
Answer: When a thread terminates its processing, it enters the dead state.

Question: How does Java handle integer overflows and underflows?
Answer: It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

Question: What is the difference between the >> and >>> operators?
Answer: The >> operator carries the sign bit when shifting right. The >>> zero-fills bits that have been shifted out.

Question: Is sizeof a keyword?
Answer: The sizeof operator is not a keyword.

Question: Does garbage collection guarantee that a program will not run out of memory?
Answer: Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection


Question: Can an object's finalize() method be invoked while it is reachable?
Answer: An object's finalize() method cannot be invoked by the garbage collector while the object is still reachable. However, an object's finalize() method may be invoked by other objects.

Question: What value does readLine() return when it has reached the end of a file?
Answer: The readLine() method returns null when it has reached the end of a file.

Question: Can a for statement loop indefinitely?
Answer: Yes, a for statement can loop indefinitely. For example, consider the following: for(;;) ;

Question: To what value is a variable of the String type automatically initialized?
Answer: The default value of an String type is null.

Question: What is a task's priority and how is it used in scheduling?
Answer: A task's priority is an integer value that identifies the relative order in which it should be executed with respect to other tasks. The scheduler attempts to schedule higher priority tasks before lower priority tasks.

Question: What is the range of the short type?
Answer: The range of the short type is -(2^15) to 2^15 - 1.

Question: What is the purpose of garbage collection?
Answer: The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources may be reclaimed and reused.

Question: How may messaging models do JMS provide for and what are they?

Answer: JMS provide for two messaging models, publish-and-subscribe and point-to-point queuing

Question: What information is needed to create a TCP Socket? (Networking)
Answer: The Local System?s IP Address and Port Number. And the Remote System's IPAddress and Port Number.

Question: What Class.forName will do while loading drivers? (JDBC)
Answer: It is used to create an instance of a driver and register it with the DriverManager. When you have loaded a driver, it is available for making a connection with a DBMS.

Question: How to Retrieve Warnings? (JDBC)
Answer: SQLWarning objects are a subclass of SQLException that deal with database access warnings. Warnings do not stop the execution of an application, as exceptions do; they simply alert the user that something did not happen as planned. A warning can be reported on a Connection object, a Statement object (including PreparedStatement and CallableStatement objects), or a ResultSet object. Each of these classes has a getWarnings method, which you must invoke in order to see the first warning reported on the calling object
E.g.
SQLWarning warning = stmt.getWarnings();
if (warning != null) {
while (warning != null) {
System.out.println("Message: " + warning.getMessage());
System.out.println("SQLState: " + warning.getSQLState());
System.out.print("Vendor error code: ");
System.out.println(warning.getErrorCode());
warning = warning.getNextWarning();
}
}

Question: How many JSP scripting elements are there and what are they? (JSP)
Answer: There are three scripting language elements:
declarations
scriptlets
expressions

Question: In the Servlet 2.4 specification SingleThreadModel has been deprecates, why? (JSP)
Answer: Because it is not practical to have such model. Whether you set isThreadSafe to true or false, you should take care of concurrent client requests to the JSP page by synchronizing access to any shared objects defined at the page level.

Question: what are stored procedures? How is it useful? (JDBC)
Answer: A stored procedure is a set of statements/commands which reside in the database. The stored procedure is precompiled and saves the database the effort of parsing and compiling sql statements everytime a query is run. Each Database has it's own stored procedure language, usually a variant of C with a SQL preproceesor. Newer versions of db's support writing stored procs in Java and Perl too.
Before the advent of 3-tier/n-tier architecture it was pretty common for stored procs to implement the business logic( A lot of systems still do it). The biggest advantage is of course speed. Also certain kind of data manipulations are not achieved in SQL. Stored procs provide a mechanism to do these manipulations. Stored procs are also useful when you want to do Batch updates/exports/houseKeeping kind of stuff on the db. The overhead of a JDBC Connection may be significant in these cases.

Question: What do you understand by private, protected and public?
Answer: These are accessibility modifiers. Private is the most restrictive, while public is the least restrictive. There is no real difference between protected and the default type (also known as package protected) within the context of the same package, however the protected keyword allows visibility to a derived class in a different package.

Question: What is Downcasting ?
Answer: Downcasting is the casting from a general to a more specific type, i.e. casting down the hierarchy

Question: Can a method be overloaded based on different return type but same argument type ?
Answer: No, because the methods can be called without using their return type in which case there is ambiquity for the compiler

Question: What happens to a static var that is defined within a method of a class ?
Answer: Can't do it. You'll get a compilation error

Question: How many static init can you have ?
Answer: As many as you want, but the static initializers and class variable initializers are executed in textual order and may not refer to class variables declared in the class whose declarations appear textually after the use, even though these class variables are in scope.

Question: What is the difference amongst JVM Spec, JVM Implementation, JVM Runtime ?
Answer: The JVM spec is the blueprint for the JVM generated and owned by Sun. The JVM implementation is the actual implementation of the spec by a vendor and the JVM runtime is the actual running instance of a JVM implementation
Question: Describe what happens when an object is created in Java?
Answer: Several things happen in a particular order to ensure the object is constructed properly:
1. Memory is allocated from heap to hold all instance variables and implementation-specific data of the object and its superclasses. Implemenation-specific data includes pointers to class and method data.
2. The instance variables of the objects are initialized to their default values.
3. The constructor for the most derived class is invoked. The first thing a constructor does is call the consctructor for its superclasses. This process continues until the constrcutor for java.lang.Object is called, as java.lang.Object is the base class for all objects in java.
4. Before the body of the constructor is executed, all instance variable initializers and initialization blocks are executed. Then the body of the constructor is executed. Thus, the constructor for the base class completes first and constructor for the most derived class completes last.

Question: What does the "final" keyword mean in front of a variable? A method? A class?
Answer: FINAL for a variable : value is constant
FINAL for a method : cannot be overridden
FINAL for a class : cannot be derived

Question: What is the difference between instanceof and isInstance?
Answer: instanceof is used to check to see if an object can be cast into a specified type without throwing a cast class exception.
isInstance()
Determines if the specified Object is assignment-compatible with the object represented by this Class. This method is the dynamic equivalent of the Java language instanceof operator. The method returns true if the specified Object argument is non-null and can be cast to the reference type represented by this Class object without raising a ClassCastException. It returns false otherwise.

Question: Wha is the output from System.out.println("Hello"+null);

Answer: Hellonull

Question: Whats the difference between notify() and notifyAll()?
Answer: notify() is used to unblock one waiting thread; notifyAll() is used to unblock all of them. Using notify() is preferable (for efficiency) when only one blocked thread can benefit from the change (for example, when freeing a buffer back into a pool). notifyAll() is necessary (for correctness) if multiple threads should resume (for example, when releasing a "writer" lock on a file might permit all "readers" to resume).

Question: Why can't I say just abs() or sin() instead of Math.abs() and Math.sin()?
Answer: The import statement does not bring methods into your local name space. It lets you abbreviate class names, but not get rid of them altogether. That's just the way it works, you'll get used to it. It's really a lot safer this way.
However, there is actually a little trick you can use in some cases that gets you what you want. If your top-level class doesn't need to inherit from anything else, make it inherit from java.lang.Math. That *does* bring all the methods into your local name space. But you can't use this trick in an applet, because you have to inherit from java.awt.Applet. And actually, you can't use it on java.lang.Math at all, because Math is a "final" class which means it can't be extended.

Question: Is "abc" a primitive value?
Answer: The String literal "abc" is not a primitive value. It is a String object.

Question: What restrictions are placed on the values of each case of a switch statement?

Answer: During compilation, the values of each case of a switch statement must evaluate to a value that can be promoted to an int value.

Question: What modifiers may be used with an interface declaration?
Answer: An interface may be declared as public or abstract.

Question: Is a class a subclass of itself?
Answer: A class is a subclass of itself.

Question: What is the difference between a while statement and a do statement?
Answer: A while statement checks at the beginning of a loop to see whether the next loop iteration should occur. A do statement checks at the end of a loop to see whether the next iteration of a loop should occur. The do statement will always execute the body of a loop at least once.

Question: What modifiers can be used with a local inner class?
Answer: A local inner class may be final or abstract.

Question: What is the purpose of the File class?
Answer: The File class is used to create objects that provide access to the files and directories of a local file system.

Question: Can an exception be rethrown?
Answer: Yes, an exception can be rethrown.

Question: When does the compiler supply a default constructor for a class?
Answer: The compiler supplies a default constructor for a class if no other constructors are provided.

Question: If a method is declared as protected, where may the method be accessed?
Answer: A protected method may only be accessed by classes or interfaces of the same package or by subclasses of the class in which it is declared.

Question: Which non-Unicode letter characters may be used as the first character of an identifier?
Answer: The non-Unicode letter characters $ and _ may appear as the first character of an identifier

Question: What restrictions are placed on method overloading?
Answer: Two methods may not have the same name and argument list but different return types.

Question: What is casting?
Answer: There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.

Question: What is the return type of a program's main() method?
Answer: A program's main() method has a void return type.

Question: What class of exceptions are generated by the Java run-time system?
Answer: The Java runtime system generates RuntimeException and Error exceptions.

Question: What class allows you to read objects directly from a stream?
Answer: The ObjectInputStream class supports the reading of objects from input streams.

Question: What is the difference between a field variable and a local variable?
Answer: A field variable is a variable that is declared as a member of a class. A local variable is a variable that is declared local to a method.

Question: How are this() and super() used with constructors?
Answer: this() is used to invoke a constructor of the same class. super() is used to invoke a superclass constructor.

Question: What is the relationship between a method's throws clause and the exceptions that can be thrown during the method's execution?

Answer: A method's throws clause must declare any checked exceptions that are not caught within the body of the method.

Question: Why are the methods of the Math class static?
Answer: So they can be invoked as if they are a mathematical code library.

Question: What are the legal operands of the instanceof operator?
Answer: The left operand is an object reference or null value and the right operand is a class, interface, or array type.

Question: What an I/O filter?
Answer: An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.

Question: If an object is garbage collected, can it become reachable again?
Answer: Once an object is garbage collected, it ceases to exist. It can no longer become reachable again.

Question: What are E and PI?
Answer: E is the base of the natural logarithm and PI is mathematical value pi.

Question: Are true and false keywords?
Answer: The values true and false are not keywords.

Question: What is the difference between the File and RandomAccessFile classes?
Answer: The File class encapsulates the files and directories of the local file system. The RandomAccessFile class provides the methods needed to directly access data contained in any part of a file.

Question: What happens when you add a double value to a String?
Answer: The result is a String object.

Question: What is your platform's default character encoding?
Answer: If you are running Java on English Windows platforms, it is probably Cp1252.
If you are running Java on English Solaris platforms, it is most likely 8859_1.

Question: Which package is always imported by default?
Answer: The java.lang package is always imported by default.

Question: What interface must an object implement before it can be written to a stream as an object?
Answer: An object must implement the Serializable or Externalizable interface before it can be written to a stream as an object.

Core Java FAQ's

1.what is a transient variable?
A transient variable is a variable that may not be serialized.
2.which containers use a border Layout as their default layout?
The window, Frame and Dialog classes use a border layout as their default layout.
3.Why do threads block on I/O?
Threads block on i/o (that is enters the waiting state) so that other threads may execute while the i/o Operation is performed.
4. How are Observer and Observable used?
Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.
5. What is synchronization and why is it important?
With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object's value. This often leads to significant errors.
6. Can a lock be acquired on a class?
Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.
7. What's new with the stop(), suspend() and resume() methods in JDK 1.2?
The stop(), suspend() and resume() methods have been deprecated in JDK 1.2.
8. Is null a keyword?
The null value is not a keyword.
9. What is the preferred size of a component?
The preferred size of a component is the minimum component size that will allow the component to display normally.
10. What method is used to specify a container's layout?
The setLayout() method is used to specify a container's layout.
11. Which containers use a FlowLayout as their default layout?
The Panel and Applet classes use the FlowLayout as their default layout.
12. What state does a thread enter when it terminates its processing?
When a thread terminates its processing, it enters the dead state.
13. What is the Collections API?
The Collections API is a set of classes and interfaces that support operations on collections of objects.
14. Which characters may be used as the second character of an identifier, but not as the first character of an identifier?
The digits 0 through 9 may not be used as the first character of an identifier but they may be used after the first character of an identifier.
15. What is the List interface?
The List interface provides support for ordered collections of objects.
16. How does Java handle integer overflows and underflows?
It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.
17. What is the Vector class?
The Vector class provides the capability to implement a growable array of objects
18. What modifiers may be used with an inner class that is a member of an outer class?
A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.
19. What is an Iterator interface?
The Iterator interface is used to step through the elements of a Collection.
20. What is the difference between the >> and >>> operators?
The >> operator carries the sign bit when shifting right. The >>> zero-fills bits that have been shifted out.
21. Which method of the Component class is used to set the position and size of a component?
setBounds()
22. How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?
Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.
23What is the difference between yielding and sleeping?
When a task invokes its yield() method, it returns to the ready state. When a task invokes its sleep() method, it returns to the waiting state.
24. Which java.util classes and interfaces support event handling?
The EventObject class and the EventListener interface support event processing.
25. Is sizeof a keyword?
The sizeof operator is not a keyword.
26. What are wrapped classes?
Wrapped classes are classes that allow primitive types to be accessed as objects.
27. Does garbage collection guarantee that a program will not run out of memory?
Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection
28. What restrictions are placed on the location of a package statement within a source code file?
A package statement must appear as the first line in a source code file (excluding blank lines and comments).
29. Can an object's finalize() method be invoked while it is reachable?
An object's finalize() method cannot be invoked by the garbage collector while the object is still reachable. However, an object's finalize() method may be invoked by other objects.
30. What is the immediate superclass of the Applet class?
Panel
31. What is the difference between preemptive scheduling and time slicing?
Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.
32. Name three Component subclasses that support painting.
The Canvas, Frame, Panel, and Applet classes support painting.
33. What value does readLine() return when it has reached the end of a file?
The readLine() method returns null when it has reached the end of a file.
34. What is the immediate superclass of the Dialog class?
Window
35. What is clipping?
Clipping is the process of confining paint operations to a limited area or shape.
36. What is a native method?
A native method is a method that is implemented in a language other than Java.
37. Can a for statement loop indefinitely?
Yes, a for statement can loop indefinitely. For example, consider the following: for(;;) ;
38. What are order of precedence and associativity, and how are they used?
Order of precedence determines the order in which operators are evaluated in expressions. Associatity determines whether an expression is evaluated left-to-right or right-to-left
39. When a thread blocks on I/O, what state does it enter?
A thread enters the waiting state when it blocks on I/O.
40. To what value is a variable of the String type automatically initialized?
The default value of an String type is null.
41. What is the catch or declare rule for method declarations?
If a checked exception may be thrown within the body of a method, the method must either catch the exception or declare it in its throws clause.
42. What is the difference between a MenuItem and a CheckboxMenuItem?
The CheckboxMenuItem class extends the MenuItem class to support a menu item that may be checked or unchecked.
43. What is a task's priority and how is it used in scheduling?
A task's priority is an integer value that identifies the relative order in which it should be executed with respect to other tasks. The scheduler attempts to schedule higher priority tasks before lower priority tasks.
44. What class is the top of the AWT event hierarchy?
The java.awt.AWTEvent class is the highest-level class in the AWT event-class hierarchy.
45. When a thread is created and started, what is its initial state?
A thread is in the ready state after it has been created and started.
46. Can an anonymous class be declared as implementing an interface and extending a class?
An anonymous class may implement an interface or extend a superclass, but may not be declared to do both.
47. What is the range of the short type?
The range of the short type is -(2^15) to 2^15 - 1.
48. What is the range of the char type?
The range of the char type is 0 to 2^16 - 1.
49. In which package are most of the AWT events that support the event-delegation model defined?
Most of the AWT-related events of the event-delegation model are defined in the java.awt.event package. The AWTEvent class is defined in the java.awt package.
50. What is the immediate superclass of Menu?
MenuItem
51. What is the purpose of finalization?
The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected.
52. Which class is the immediate superclass of the MenuComponent class.
Object
53. What invokes a thread's run() method?
After a thread is started, via its start() method or that of the Thread class, the JVM invokes the thread's run() method when the thread is initially executed.
54. What is the difference between the Boolean & operator and the && operator?
If an expression involving the Boolean & operator is evaluated, both operands are evaluated. Then the & operator is applied to the operand. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. The && operator is then applied to the first and second operands. If the first operand evaluates to false, the evaluation of the second operand is skipped.
55. Name three subclasses of the Component class.
Box.Filler, Button, Canvas, Checkbox, Choice, Container, Label, List, Scrollbar, or TextComponent
56. What is the GregorianCalendar class?
The GregorianCalendar provides support for traditional Western calendars.
57. Which Container method is used to cause a container to be laid out and redisplayed?
validate()
58. What is the purpose of the Runtime class?
The purpose of the Runtime class is to provide access to the Java runtime system.
59. How many times may an object's finalize() method be invoked by the garbage collector?
An object's finalize() method may only be invoked once by the garbage collector.
60. What is the purpose of the finally clause of a try-catch-finally statement?
The finally clause is used to provide the capability to execute code no matter whether or not an exception is thrown or caught.
61. What is the argument type of a program's main() method?
A program's main() method takes an argument of the String[] type.
62. Which Java operator is right associative?
The = operator is right associative.
63. What is the Locale class?
The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region.
64. Can a double value be cast to a byte?
Yes, a double value can be cast to a byte.
65. What is the difference between a break statement and a continue statement?
A break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement.
66. What must a class do to implement an interface?
It must provide all of the methods in the interface and identify the interface in its implements clause.
67. What method is invoked to cause an object to begin executing as a separate thread?
The start() method of the Thread class is invoked to cause an object to begin executing as a separate thread.
68. Name two subclasses of the TextComponent class.
TextField and TextArea
69. What is the advantage of the event-delegation model over the earlier event-inheritance model?
The event-delegation model has two advantages over the event-inheritance model. First, it enables event handling to be handled by objects other than the ones that generate the events (or their containers). This allows a clean separation between a component's design and its use. The other advantage of the event-delegation model is that it performs much better in applications where many events are generated. This performance improvement is due to the fact that the event-delegation model does not have to repeatedly process unhandled events, as is the case of the event-inheritance model.
70. Which containers may have a MenuBar?
Frame
71. How are commas used in the intialization and iteration parts of a for statement?
Commas are used to separate multiple statements within the initialization and iteration parts of a for statement.
72. What is the purpose of the wait(), notify(), and notifyAll() methods?
The wait(),notify(), and notifyAll() methods are used to provide an efficient way for threads to wait for a shared resource. When a thread executes an object's wait() method, it enters the waiting state. It only enters the ready state after another thread invokes the object's notify() or notifyAll() methods.
73. What is an abstract method?
An abstract method is a method whose implementation is deferred to a subclass.
74. How are Java source code files named?
A Java source code file takes the name of a public class or interface that is defined within the file. A source code file may contain at most one public class or interface. If a public class or interface is defined within a source code file, then the source code file must take the name of the public class or interface. If no public class or interface is defined within a source code file, then the file must take on a name that is different than its classes and interfaces. Source code files use the .java extension.
75. What is the relationship between the Canvas class and the Graphics class?
A Canvas object provides access to a Graphics object via its paint() method.
76. What are the high-level thread states?
The high-level thread states are ready, running, waiting, and dead.
77. What value does read() return when it has reached the end of a file?
The read() method returns -1 when it has reached the end of a file.
78. Can a Byte object be cast to a double value?
No, an object cannot be cast to a primitive value.
79. What is the difference between a static and a non-static inner class?
A non-static inner class may have object instances that are associated with instances of the class's outer class. A static inner class does not have any object instances.
80. What is the difference between the String and StringBuffer classes?
String objects are constants. StringBuffer objects are not.
81. If a variable is declared as private, where may the variable be accessed?
A private variable may only be accessed within the class in which it is declared.
82. What is an object's lock and which object's have locks?
An object's lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. A thread may execute a synchronized method of an object only after it has acquired the object's lock. All objects and classes have locks. A class's lock is acquired on the class's Class object.
83. What is the Dictionary class?
The Dictionary class provides the capability to store key-value pairs.
84. How are the elements of a BorderLayout organized?
The elements of a BorderLayout are organized at the borders (North, South, East, and West) and the center of a container.
85. What is the % operator?
It is referred to as the modulo or remainder operator. It returns the remainder of dividing the first operand by the second operand.
86. When can an object reference be cast to an interface reference?
An object reference be cast to an interface reference when the object implements the referenced interface.
87. What is the difference between a Window and a Frame?
The Frame class extends Window to define a main application window that can have a menu bar.
88. Which class is extended by all other classes?
The Object class is extended by all other classes.
89. Can an object be garbage collected while it is still reachable?
A reachable object cannot be garbage collected. Only unreachable objects may be garbage collected..
90. Is the ternary operator written x : y ? z or x ? y : z ?
It is written x ? y : z.
91. What is the difference between the Font and FontMetrics classes?
The FontMetrics class is used to define implementation-specific properties, such as ascent and descent, of a Font object.
92. How is rounding performed under integer division?
The fractional part of the result is truncated. This is known as rounding toward zero.
93. What happens when a thread cannot acquire a lock on an object?
If a thread attempts to execute a synchronized method or synchronized statement and is unable to acquire an object's lock, it enters the waiting state until the lock becomes available.
94. What is the difference between the Reader/Writer class hierarchy and the InputStream/OutputStream class hierarchy?
The Reader/Writer class hierarchy is character-oriented, and the InputStream/OutputStream class hierarchy is byte-oriented.
95. What classes of exceptions may be caught by a catch clause?
A catch clause can catch any exception that may be assigned to the Throwable type. This includes the Error and Exception types.
96. If a class is declared without any access modifiers, where may the class be accessed?
A class that is declared without any access modifiers is said to have package access. This means that the class can only be accessed by other classes and interfaces that are defined within the same package.
97. What is the SimpleTimeZone class?
The SimpleTimeZone class provides support for a Gregorian calendar.
98. What is the Map interface?
The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values.
99. Does a class inherit the constructors of its superclass?
A class does not inherit constructors from any of its superclasses.
100. For which statements does it make sense to use a label?
The only statements for which it makes sense to use a label are those statements that can enclose a break or continue statement.
101. What is the purpose of the System class?
The purpose of the System class is to provide access to system resources.
102. Which TextComponent method is used to set a TextComponent to the read-only state?
setEditable()
103. How are the elements of a CardLayout organized?
The elements of a CardLayout are stacked, one on top of the other, like a deck of cards.
104. Is &&= a valid Java operator?
No, it is not.
105. Name the eight primitive Java types.
The eight primitive types are byte, char, short, int, long, float, double, and boolean.
106. Which class should you use to obtain design information about an object?
The Class class is used to obtain information about an object's design.
107. What is the relationship between clipping and repainting?
When a window is repainted by the AWT painting thread, it sets the clipping regions to the area of the window that requires repainting.
108. Is "abc" a primitive value?
The String literal "abc" is not a primitive value. It is a String object.
109. What is the relationship between an event-listener interface and an event-adapter class?
An event-listener interface defines the methods that must be implemented by an event handler for a particular kind of event. An event adapter provides a default implementation of an event-listener interface.
110. What restrictions are placed on the values of each case of a switch statement?
During compilation, the values of each case of a switch statement must evaluate to a value that can be promoted to an int value.
111. What modifiers may be used with an interface declaration?
An interface may be declared as public or abstract.
112. Is a class a subclass of itself?
A class is a subclass of itself.
113. What is the highest-level event class of the event-delegation model?
The java.util.EventObject class is the highest-level class in the event-delegation class hierarchy.
114. What event results from the clicking of a button?
The ActionEvent event is generated as the result of the clicking of a button.
115. How can a GUI component handle its own events?
A component can handle its own events by implementing the required event-listener interface and adding itself as its own event listener.
116. What is the difference between a while statement and a do statement?
A while statement checks at the beginning of a loop to see whether the next loop iteration should occur. A do statement checks at the end of a loop to see whether the next iteration of a loop should occur. The do statement will always execute the body of a loop at least once.
117. How are the elements of a GridBagLayout organized?
The elements of a GridBagLayout are organized according to a grid. However, the elements are of different sizes and may occupy more than one row or column of the grid. In addition, the rows and columns may have different sizes.
118. What advantage do Java's layout managers provide over traditional windowing systems?
Java uses layout managers to lay out components in a consistent manner across all windowing platforms. Since Java's layout managers aren't tied to absolute sizing and positioning, they are able to accomodate platform-specific differences among windowing systems.
119. What is the Collection interface?
The Collection interface provides support for the implementation of a mathematical bag - an unordered collection of objects that may contain duplicates.
120. What modifiers can be used with a local inner class?
A local inner class may be final or abstract.
121. What is the difference between static and non-static variables?
A static variable is associated with the class as a whole rather than with specific instances of a class. Non-static variables take on unique values with each object instance.
122. What is the difference between the paint() and repaint() methods?
The paint() method supports painting via a Graphics object. The repaint() method is used to cause paint() to be invoked by the AWT painting thread.
123. What is the purpose of the File class?
The File class is used to create objects that provide access to the files and directories of a local file system.
124. Can an exception be rethrown?
Yes, an exception can be rethrown.
125. Which Math method is used to calculate the absolute value of a number?
The abs() method is used to calculate absolute values.
126. How does multithreading take place on a computer with a single CPU?
The operating system's task scheduler allocates execution time to multiple tasks. By quickly switching between executing tasks, it creates the impression that tasks execute sequentially.
127. When does the compiler supply a default constructor for a class?
The compiler supplies a default constructor for a class if no other constructors are provided.
128. When is the finally clause of a try-catch-finally statement executed?
The finally clause of the try-catch-finally statement is always executed unless the thread of execution terminates or an exception occurs within the execution of the finally clause.
129. Which class is the immediate superclass of the Container class?
Component
130. If a method is declared as protected, where may the method be accessed?
A protected method may only be accessed by classes or interfaces of the same package or by subclasses of the class in which it is declared.
131. How can the Checkbox class be used to create a radio button?
By associating Checkbox objects with a CheckboxGroup.
132. Which non-Unicode letter characters may be used as the first character of an identifier?
The non-Unicode letter characters $ and _ may appear as the first character of an identifier
133. What restrictions are placed on method overloading?
Two methods may not have the same name and argument list but different return types.
134. What happens when you invoke a thread's interrupt method while it is sleeping or waiting?
When a task's interrupt() method is executed, the task enters the ready state. The next time the task enters the running state, an InterruptedException is thrown.
135. What is casting?
There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.
136. What is the return type of a program's main() method?
A program's main() method has a void return type.
137. Name four Container classes.
Window, Frame, Dialog, FileDialog, Panel, Applet, or ScrollPane
138. What is the difference between a Choice and a List?
A Choice is displayed in a compact form that requires you to pull it down to see the list of available choices. Only one item may be selected from a Choice. A List may be displayed in such a way that several List items are visible. A List supports the selection of one or more List items.
139. What class of exceptions are generated by the Java run-time system?
The Java runtime system generates RuntimeException and Error exceptions.
140. What class allows you to read objects directly from a stream?
The ObjectInputStream class supports the reading of objects from input streams.
141. What is the difference between a field variable and a local variable?
A field variable is a variable that is declared as a member of a class. A local variable is a variable that is declared local to a method.
142. Under what conditions is an object's finalize() method invoked by the garbage collector?
The garbage collector invokes an object's finalize() method when it detects that the object has become unreachable.
143. How are this() and super() used with constructors?
this() is used to invoke a constructor of the same class. super() is used to invoke a superclass constructor.
144. What is the relationship between a method's throws clause and the exceptions that can be thrown during the method's execution?
A method's throws clause must declare any checked exceptions that are not caught within the body of the method.
145. What is the difference between the JDK 1.02 event model and the event-delegation model introduced with JDK 1.1?
The JDK 1.02 event model uses an event inheritance or bubbling approach. In this model, components are required to handle their own events. If they do not handle a particular event, the event is inherited by (or bubbled up to) the component's container. The container then either handles the event or it is bubbled up to its container and so on, until the highest-level container has been tried.
In the event-delegation model, specific objects are designated as event handlers for GUI components. These objects implement event-listener interfaces. The event-delegation model is more efficient than the event-inheritance model because it eliminates the processing required to support the bubbling of unhandled events.
146. How is it possible for two String objects with identical values not to be equal under the == operator?
The == operator compares two objects to determine if they are the same object in memory. It is possible for two String objects to have the same value, but located indifferent areas of memory.
147. Why are the methods of the Math class static?
So they can be invoked as if they are a mathematical code library.
148. What Checkbox method allows you to tell if a Checkbox is checked?
getState()
149. What state is a thread in when it is executing?
An executing thread is in the running state.
150. What are the legal operands of the instanceof operator?
The left operand is an object reference or null value and the right operand is a class, interface, or array type.
151. How are the elements of a GridLayout organized?
The elements of a GridBad layout are of equal size and are laid out using the squares of a grid.
152. What an I/O filter?
An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.
153. If an object is garbage collected, can it become reachable again?
Once an object is garbage collected, it ceases to exist. It can no longer become reachable again.
154. What is the Set interface?
The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements.
155. What classes of exceptions may be thrown by a throw statement?
A throw statement may throw any expression that may be assigned to the Throwable type.
156. What are E and PI?
E is the base of the natural logarithm and PI is mathematical value pi.
157. Are true and false keywords?
The values true and false are not keywords.
158. What is a void return type?
A void return type indicates that a method does not return a value.
159. What is the purpose of the enableEvents() method?
The enableEvents() method is used to enable an event for a particular object. Normally, an event is enabled when a listener is added to an object for a particular event. The enableEvents() method is used by objects that handle events by overriding their event-dispatch methods.
160. What is the difference between the File and RandomAccessFile classes?
The File class encapsulates the files and directories of the local file system. The RandomAccessFile class provides the methods needed to directly access data contained in any part of a file.
161. What happens when you add a double value to a String?
The result is a String object.
162. What is your platform's default character encoding?
If you are running Java on English Windows platforms, it is probably Cp1252. If you are running Java on English Solaris platforms, it is most likely 8859_1..
163. Which package is always imported by default?
The java.lang package is always imported by default.
164. What interface must an object implement before it can be written to a stream as an object?
An object must implement the Serializable or Externalizable interface before it can be written to a stream as an object.
165. How are this and super used?
this is used to refer to the current object instance. super is used to refer to the variables and methods of the superclass of the current object instance.
166. What is the purpose of garbage collection?
The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources may be reclaimed and reused.
167. What is a compilation unit?
A compilation unit is a Java source code file.
168. What interface is extended by AWT event listeners?
All AWT event listeners extend the java.util.EventListener interface.
169. What restrictions are placed on method overriding?
Overridden methods must have the same name, argument list, and return type. The overriding method may not limit the access of the method it overrides. The overriding method may not throw any exceptions that may not be thrown by the overridden method.
170. How can a dead thread be restarted?
A dead thread cannot be restarted.
171. What happens if an exception is not caught?
An uncaught exception results in the uncaughtException() method of the thread's ThreadGroup being invoked, which eventually results in the termination of the program in which it is thrown.
172. What is a layout manager?
A layout manager is an object that is used to organize components in a container.
173. Which arithmetic operations can result in the throwing of an ArithmeticException?
Integer / and % can result in the throwing of an ArithmeticException.
174. What are three ways in which a thread can enter the waiting state?
A thread can enter the waiting state by invoking its sleep() method, by blocking on I/O, by unsuccessfully attempting to acquire an object's lock, or by invoking an object's wait() method. It can also enter the waiting state by invoking its (deprecated) suspend() method.
175. Can an abstract class be final?
An abstract class may not be declared as final.
176. What is the ResourceBundle class?
The ResourceBundle class is used to store locale-specific resources that can be loaded by a program to tailor the program's appearance to the particular locale in which it is being run.
177. What happens if a try-catch-finally statement does not have a catch clause to handle an exception that is thrown within the body of the try statement?
The exception propagates up to the next higher level try-catch statement (if any) or results in the program's termination.
178. What is numeric promotion?
Numeric promotion is the conversion of a smaller numeric type to a larger numeric type, so that integer and floating-point operations may take place. In numerical promotion, byte, char, and short values are converted to int
values. The int values are also converted to long values, if necessary. The long and float values are converted to double values, as required.
179. What is the difference between a Scrollbar and a ScrollPane?
A Scrollbar is a Component, but not a Container. A ScrollPane is a Container. A ScrollPane handles its own events and performs its own scrolling.
180. What is the difference between a public and a non-public class?
A public class may be accessed outside of its package. A non-public class may not be accessed outside of its package.
181. To what value is a variable of the boolean type automatically initialized?
The default value of the boolean type is false.
182. Can try statements be nested?
Try statements may be tested.
183. What is the difference between the prefix and postfix forms of the ++ operator?
The prefix form performs the increment operation and returns the value of the increment operation. The postfix form returns the current value all of the expression and then performs the increment operation on that value.
184. What is the purpose of a statement block?
A statement block is used to organize a sequence of statements as a single statement group.
185. What is a Java package and how is it used?
A Java package is a naming context for classes and interfaces. A package is used to create a separate name space for groups of classes and interfaces. Packages are also used to organize related classes and interfaces into a single API unit and to control accessibility to these classes and interfaces.
186. What modifiers may be used with a top-level class?
A top-level class may be public, abstract, or final.
187. What are the Object and Class classes used for?
The Object class is the highest-level class in the Java class hierarchy. The Class class is used to represent the classes and interfaces that are loaded by a Java program.
188. How does a try statement determine which catch clause should be used to handle an exception?
When an exception is thrown within the body of a try statement, the catch clauses of the try statement are examined in the order in which they appear. The first catch clause that is capable of handling the exception is executed. The remaining catch clauses are ignored.
189. Can an unreachable object become reachable again?
An unreachable object may become reachable again. This can happen when the object's finalize() method is invoked and the object performs an operation which causes it to become accessible to reachable objects.
190. When is an object subject to garbage collection?
An object is subject to garbage collection when it becomes unreachable to the program in which it is used.
191. What method must be implemented by all threads?
All tasks must implement the run() method, whether they are a subclass of Thread or implement the Runnable interface.
192. What methods are used to get and set the text label displayed by a Button object?
getLabel() and setLabel()
193. Which Component subclass is used for drawing and painting?
Canvas
194. What are synchronized methods and synchronized statements?
Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement.
195. What are the two basic ways in which classes that can be run as threads may be defined?
A thread class may be declared as a subclass of Thread, or it may implement the Runnable interface.
196. What are the problems faced by Java programmers who don't use layout managers?
Without layout managers, Java programmers are faced with determining how their GUI will be displayed across multiple windowing systems and finding a common sizing and positioning that will work within the constraints imposed by each windowing system.
197. What is the difference between an if statement and a switch statement?
The if statement is used to select among two alternatives. It uses a boolean expression to decide which alternative should be executed. The switch statement is used to select among multiple alternatives. It uses an int expression to determine which alternative should be executed.
198. What happens when you add a double value to a String?
The result is a String object.
199. What is the List interface?
The List interface provides support for ordered collections of objects.

Java Interview Questions

Object, Class, and Methods

1.What is an object?
2.What is a class?
3.What is a method?
4.What is the signature of a method?
5.What is the difference between an instance variable and a class variable?
6.What is the difference between an instance method and a class method?
7.How do I create an instance of a class?
8.What is an abstract method?
9.What is an abstract class?
10.What is an object reference?

Subclassing, Overloading, and Overriding

1.What is a subclass?
2.What is inheritance?
3.What is an overloaded method?
4.What does it mean to override a method?
5.What is the difference between overloading and overriding?
6.Can I override the equals method or clone method from class Object to take a parameter or return a value of the type that I specify?
7.What is the super keyword used for?
8.Does the Java language provide virtual methods, like C++?
9.What is a final class?
Interfaces and Abstract Classes
1.What is an interface?
2.How does a class implement an interface?
3.Can I instantiate an interface?
4.Why does a method in an interface appear to be public even though I didn't declare it to be public?
5.How is an abstract class different from an interface?
6.Does the Java language allow multiple inheritance?
7.What is the instanceof keyword, and what does it do?
8.Why do I get the error message Can't access protected method clone... when I try to clone an object?
9.How do I design a class so that it supports cloning?

Packages and Access Modifiers

1.What are packages, and what are they used for?
2.I've seen both java.applet.Applet and Applet used to refer to the Applet class -- what's the difference?
3.Why can I get some simple class names "for free," without using an import declaration?
4.Is there a default access modifier for classes and interfaces? For class members (methods, constructors, and fields)?
5.What does protected access mean?
6.What is the accessibility of a public method or field inside a nonpublic class or interface?
Constants and Expressions
1.What is the difference between Integer and int in Java -- why do I get the following error: Can't convert java.lang.Integer to int?
2.How do I treat all 8 bits of a byte as an unsigned quantity?
3.How do I work around Java's lack of true enums?
4.Why is goto a reserved keyword in Java -- shouldn't it be outlawed?
5.What are some guidelines for using uppercase and lowercase letters in my identifiers?
6.Is there any limit to the length of an identifier?
7.Why doesn't Java have user-defined operator overloading?
8.Why do I have to put an f after a floating point constant?
9.How and when can I cast from one class to another?
10.Can I use C-like data structures in Java?

Variables and Methods

1.Are Java objects pointers?
2.In a method invocation, does Java pass arguments by reference or by value?
3.If the Java language lacks pointers, how do I implement classic pointer structures like linked lists?
4.What does the following error message mean: Can't make a static reference to nonstatic variable?
5.In a class method, how can I get the name of the class, or create a new instance of the class?
6.Can I write a method that delivers dynamically (at run time) all public methods of an object?
7.Can I invoke methods dynamically, from names (String instances) that are determined at run time?
8.How can I accomplish the equivalent of function pointers in Java, for instance, for use in an array?
Arrays
1.Can I allocate an array dynamically?
2.How do I initialize an array of objects?
3.If arrays are objects, why can't I use a length method to determine an array's size?

Exceptions

1.What is an exception?
2.Why does the compiler complain about InterruptedException when I try to use Thread's sleep method?
3.Why do methods have to declare the exceptions they can throw?
4.What's the difference between a runtime exception and a plain exception -- why don't runtime exceptions have to be declared?

Virtual Machine

1.When, and by whom, is the main method of a class invoked?
2.What are bytecodes?
3.What is javap?
4.What does it mean to say that Java is interpreted?
5.What kind of garbage collection does the Java Virtual Machine use?
6.Is finalization broken -- why does my finalize method never seem to get invoked?
7.I'm having trouble invoking methods on the objects returned from Class's forName method -- how should I use Class.forName?
8.Why do I get verifier errors when loading a class file produced by javac?
9.How fast are Java programs compared to equivalent C or C++ programs?

Applets versus Applications

1.What is an applet?
2.How do applets differ from applications?
3.Can I write Java code that works both as an applet and as a stand-alone application?
Installing Applets
1.How do I put an applet into a web page?
2.Can I put more than one applet in a web page?
3.How do I use the APPLET tag if I want to show users of non-Java-enabled browsers what they're missing?
4.What is the complete syntax for using the APPLET tag?
5.What are the different pieces that can make up an applet, and how do I install them?
6.Where can I put my applet's class files, and how do I indicate their location using the APPLET tag?
7.Can I put my reusable custom classes in a special place so that many different applets can use them?

Applet User Interface

1.How do I determine the width and height of my applet?
2.How do I set the background color within the applet area?
3.How can I create a transparent background for my applet?
4.Can I put menus and a menu bar on my applet?
5.I know that cursors can be changed from within frames, but how do I change the cursor in my applet?

Applet Program Structure

1.Several applet methods seem special, in that I need to define them even if my own code doesn't invoke them -- what are the methods, and when (and by whom) are they invoked?
2.Should applets have constructors?
3.How can my applet tell when a user leaves or returns to the web page containing my applet?
4.How do I read number information from my applet's parameters, given that Applet's getParameter method returns a String?
Applet Communication
1.How can I arrange for different applets on a web page to communicate with each other?
2.How do I select a URL from my applet and send the browser to that page?
3.Can applets on different pages communicate with each other?

Miscellaneous

1.Can I load an applet dynamically into a Java application, and if so, how does the applet get the parameter information it would normally get from the APPLET tag?
2.Do I need any special server software or setup to deliver applets?
Components, Containers, and Peers
1.What are the Component and Container classes?
2.How do I control the positioning of my interface components?
3.What are inset values, and how do I set them?
4.Can I exert complete control over the size and placement of components in my interface?
5.What do the invalidate and validate methods do?
6.Can I add new AWT components to objects already visible on the screen?
7.Can I add the same component to more than one container?
8.How can I place an outline around a group of components to show explicitly how the components are grouped?

9.What are AWT peers?

Windows, Frames, and Dialogs

1.How do I specify where a window is to be placed?
2.How can I draw at the top-left corner of a frame without it being covered by the frame's border?
3.How do I create a borderless window?
4.Several operations in the AWT, such as setting the cursor (in JDK 1.0.2) or creating a dialog box, require specifying a Frame instance -- how do I determine the Frame instance containing the current component?
5.How do I use a FileDialog object in my applet or application?
6.Can I create nonresizable windows?

Miscellaneous

1.What does Component's requestFocus method do?
2.Does the AWT allow you to control the mouse location from within an application?
3.Does the AWT provide a standard way to signal a user error by flashing, beeping, or some other means?
4.What fonts are available to my AWT program?
5.How can I dynamically change font attributes, for instance, rendering a string in successively larger font sizes?
Events -- JDK 1.0.2
1.What information can be carried in the JDK 1.0.2 by an Event object?
2.What information do specific event types in the JDK 1.0.2 carry?
3.What is the general model in the JDK 1.0.2 for distributing and handling events?
4.What methods should I use in the JDK 1.0.2 to handle events?
5.What is an action event?
6.How does the JDK 1.0.2 handle events for function keys, arrow keys, and so on?
7.My frame doesn't close when I click on Quit/Close in the main menu -- how do I fix this using JDK 1.0.2?
8.How is my program notified when a menu item is selected?
9.MenuItemEventExample.html
10.How is my program notified in the JDK 1.0.2 when a list item is selected or deselected?
11.How do I hook up a scroll bar in the JDK 1.0.2 so that it controls the scrolling of some other component?
12.Does the AWT in the JDK 1.0.2 distinguish between mouse clicks made with different buttons on a two- or three-button mouse?

Event Classes, Listeners, and Methods

1.What information do specific event types in the JDK 1.1 carry?
2.How do I catch events in the JDK 1.1 event model?
3.What are the different kinds of event listeners, and what are their methods?
4.When should I use an event adapter class?
5.Do events propagate in the JDK 1.1 as they did in the older AWT event model?
6.Will my code written for the older JDK 1.0.2 event model still run in the JDK 1.1?
SEMANTIC EVENTS
1.How do I handle action events in the JDK 1.1?
2.How do I catch menu item events in the 1.1 AWT event model?
3.In the JDK 1.1 AWT event model, how is my program notified when a list item is selected or deselected?
4.How do I control scrolling in the 1.1 AWT?

LOW-LEVEL EVENTS

1.My frame doesn't close when I click on Quit/Close in the main menu -- how do I fix this using the JDK 1.1?
2.Is there an event type that signals when a window is resized?
3.How do I handle events for function keys, arrow keys, and so on in the JDK 1.1 event model?
4.How does the JDK 1.1 distinguish between mouse clicks made with different buttons on a two- or three-button mouse?

Drawing AWT Components

1.What is the paint method for, when is it invoked, and by whom?
2.What should I put in my paint method?
3.What is repaint for, when is it invoked, and by whom?
4.Why do my repeated calls to repaint not have any effect?
5.What is update for, when is it invoked, and by whom?
6.What drawing occurs if my applet or other component reappears after being covered by some other window?
7.Can I implement an invisible or partly transparent component?
8.How does the XOR drawing mode work?
Loading and Drawing Images
1.How do I load an image from the net into my applet?
2.How do I load an image from a file in a stand-alone Java application, rather than in an applet?
3.When is an image actually loaded -- why not immediately?
4.How can I make sure that my images are completely loaded before I check for their data or parameters?
5.Why does my call to Graphics's drawImage method fail to show the image?
6.Can I force Applet's getImage method to make a new connection for each image rather than reusing a cached version of the image?
7.How do I draw text over a background image?
8.How do I load and display a transparent GIF image over a background image?
9.How can I create an image from a buffer of raw image data (red, green, and blue values for each pixel)?
10.What is double buffering -- how can I create and draw to an offscreen image?
11.How can I get at the raw data of an image, such as the pixel value at a given coordinate?
Images -- JDK 1.0.2

1.Using the JDK 1.0.2, can I clear or reset a clipping rectangle that either I or the system has created?
2.Using the JDK 1.0.2, can I copy a subarea of one image into another image?
Images -- JDK 1.1
1.How do I control animation with MemoryImageSource?
2.Using the JDK 1.1, how do I reset a clipping rectangle?
3.What's the best way in JDK 1.1 to draw just a subarea of an image?

Creating and Controlling Threads

1.What is a thread?
2.How do I create a thread and start it running?
3.How does Thread's stop method work -- can I restart a stopped thread?
4.How should I stop a thread so that I can start a new thread later in its place?
5.How do I specify pause times in my program?
Thread Interactions
1.Why is thread synchronization important for multithreaded programs?
2.What is a monitor?
3.How does the synchronized keyword work?
4.What objects do static synchronized methods use for locking?
5.How do the wait and notifyAll/notify methods enable cooperation between threads?
6.How do I achieve the effect of condition variables if the Java platform provides me with only wait and notifyAll/notify methods?
7.How do I make one thread wait for one or more other threads to finish?
8.What do I use the yield method for?
9.Does the Java Virtual Machine protect me against deadlocks?

User Threads versus System Threads

1.Why does my multithreaded program run fine on Windows NT/95 but block on Solaris?
2.Why do so many applets run a copy of themselves in a separate thread rather than just running as they are?
3.How can it be that putting an applet thread to sleep in the wrong place can block other applets from running?
4.Can I have a thread wait on an event from the operating system?

Basic Input and Output

1.How do I read a line of input at a time?
2.Why doesn't String's replace method have any effect when I apply it to a string?
3.How can I access native operating system calls from my Java program?
4.Does Java provide standard iterator functions for inspecting a collection of objects?
5.The Math.random method is too limited for my needs -- how can I generate random numbers more flexibly?

Audio

1.How do I play sounds in an applet?
2.How do I play several audio clips simultaneously?
3.Can I tell when an audio clip has finished playing?
4.How can I play audio in a stand-alone application?
5.What audio formats does the

Java Interview Questions2

Interview Type of Questions

1.What is meant by Java ?
2.What is meant by a class ?
3.What is meant by a method ?
4.What are the OOPS concepts in Java ?
5.What is meant by encapsulation ? Explain with an example
6.What is meant by inheritance ? Explain with an example
7.What is meant by polymorphism ? Explain with an example
8.Is multiple inheritance allowed in Java ? Why ?
9.What is meant by Java interpreter ?
10.What is meant by JVM ?
11.What is a compilation unit ?
12.What is meant by identifiers ?
13.What are the different types of modifiers ?
14.What are the access modifiers in Java ?
15.What are the primitive data types in Java ?
16.What is meant by a wrapper class ?
17.What is meant by static variable and static method ?
18.What is meant by Garbage collection ?
19.What is meant by abstract class
20.What is meant by final class, methods and variables ?
21.What is meant by interface ?
22.What is meant by a resource leak ?
23.What is the difference between interface and abstract class ?
24.What is the difference between public private, protected and static
25.What is meant by method overloading ?
26.What is meant by method overriding ?
27.What is singleton class ?
28.What is the difference between an array and a vector ?
29.What is meant by constructor ?
30.What is meant by casting ?
31.What is the difference between final, finally and finalize ?
32.What is meant by packages ?
33.What are all the packages ?
34.Name 2 calsses you have used ?
35.Name 2 classes that can store arbitrary number of objects ?
36.What is the difference between java.applet.* and java.applet.Applet ?
37.What is a default package ?
38.What is meant by a super class and how can you call a super class ?
39.What is anonymous class ?
40.Name interfaces without a method ?
41.What is the use of an interface ?
42.What is a serializable interface ?
43.How to prevent field from serialization ?
44.What is meant by exception ?
45.How can you avoid the runtime exception ?
46.What is the difference between throw and throws ?
47.What is the use of finally ?
48.Can multiple catch statements be used in exceptions ?
49.Is it possible to write a try within a try statement ?
50.What is the method to find if the object exited or not ?
51.What is meant by a Thread ?
52.What is meant by multi-threading ?
53.What is the 2 way of creating a thread ? Which is the best way and why ?
54.What is the method to find if a thread is active or not ?
55.What are the thread-to-thread communcation ?
56.What is the difference between sleep and suspend ?
57.Can thread become a member of another thread ?
58.What is meant by deadlock ?
59.How can you avoid a deadlock ?
60.What are the three typs of priority ?
61.What is the use of synchronizations ?
62.Garbage collector thread belongs to which priority ?
63.What is meant by time-slicing ?
64.What is the use of ‘this’ ?
65.How can you find the length and capacity of a string buffer ?
66.How to compare two strings ?
67.What are the interfaces defined by Java.lang ?
68.What is the purpose of run-time class and system class
69.What is meant by Stream and Types ?
70.What is the method used to clear the buffer ?
71.What is meant by Stream Tokenizer ?
72.What is serialization and de-serialisation ?
73.What is meant by Applet ?
74.How to find the host from which the Applet has originated ?
75.What is the life cycle of an Applet ?
76.How do you load an HTML page from an Applet ?
77.What is meant by Applet Stub Interface ?
78.What is meant by getCodeBase and getDocumentBase method ?
79.How can you call an applet from a HTML file
80.What is meant by Applet Flickering ?
81.What is the use of parameter tag ?
82.What is audio clip Interface and what are all the methods in it ?
83.What is the difference between getAppletInfo and getParameterInfo ?
84.How to communicate between applet and an applet ?
85.What is meant by event handling ?
86.What are all the listeners in java and explain ?
87.What is meant by an adapter class ?
88.What are the types of mouse event listeners ?
89.What are the types of methods in mouse listeners ?
90.What is the difference between panel and frame ?
91.What is the default layout of the panel and frame ?
92.What is meant by controls and types ?
93.What is the difference between a scroll bar and a scroll panel.
94.What is the difference between list and choice ?
95.How to place a component on Windows ?
96.What are the different types of Layouts ?
97.What is meant by CardLayout ?
98.What is the difference between GridLayout and GridBagLayout
99.What is the difference between menuitem and checkboxmenu item.
100.What is meant by vector class, dictionary class , hash table class,and property class ?
101.Which class has no duplicate elements ?
102.What is resource bundle ?
103.What is an enumeration class ?
104.What is meant by Swing ?
105.What is the difference between AWT and Swing ?
106.What is the difference between an applet and a Japplet
107.What are all the components used in Swing ?
108.What is meant by tab pans ?
109.What is the use of JTree ?
110.How can you add and remove nodes in Jtree.
111.What is the method to expand and collapse nodes in a Jtree ?
112.What is the use of JTable ?
113.What is meant by JFC ?
114.What is the class in Swing to change the appearance of the Frame in Runtime.
115.How to reduce flicking in animation ?
116.What is JDBC ?
117.How do you connect to the database ? What are the steps ?
118.What are the drivers available in JDBC ? Explain
119.How can you load the driver ?
120.What are the different types of statement s ?
121.How can you created JDBC statements ?
122.How will you perform transactions using JDBC ?
123.What are the two drivers for web apllication?
124.What are the different types of 2 tier and 3 tier architecture ?
125.How can you retrieve warning in JDBC ?
126.What is the exception thrown by JDBC ?
127.What is meants by PreparedStatement ?
128.What is difference between PreparedStatement and Statement ?
129.How can you call the stored procedures ?
130.What is meant by a ResultSet ?
131.What is the difference between ExecuteUpdate and ExecuteQuery ?
132.How do you know which driver is connected to a database ?
133.What is DSN and System DSN and differentiate these two ?
134.What is meant by TCP, IP, UDP ?
135.What is the difference between TCP and UDP ?
136.What is a proxy server ?
137.What is meant by URL
138.What is a socket and server sockets ?
139.When MalformedURLException and UnknownHost Exception throws ?
140.What is InetAddress ?
141.What is datagram and datagram packets and datagram sockets ?
142.Write the range of multicast socket IP address ?
143.What is meant by a servlet ?
144.What are the types of servlets ? Explain
145.What is the different between a Servlet and a CGI.
146.What is the difference between 2 types of Servlets ?
147.What is the type of method for sending request from HTTP server ?
148.What are the exceptions thrown by Servlets ? Why ?
149.What is the life cycle of a servlet ?
150.What is meant by cookies ?
151.What is HTTP Session ?
152.What is the difference between GET and POST methods ?
153.How can you run a Servlet Program ?
154.How to commuincate between an applet and a servlet ?
155.What is a Servlet-to-Servlet communcation ?
156.What is Session Tracking ?
157.What are the security issues in Servlets ?
158.What is HTTP Tunneling
159.How do you load an image in a Servlet ?
160.What is Servlet Chaining ?
161.What is URL Rewriting ?
162.What is context switching ?
163.What is meant by RMI ?
164.Explain RMI Architecture ?
165.What is meant by a stub ?
166.What is meant by a skelotn ?
167.What is meant by serialisation and deserialisation ?
168.What is meant by RRL ?
169.What is the use of TL ?
170.What is RMI Registry ?
171.What is rmic ?
172.How will you pass parameter in RMI ?
173.What exceptions are thrown by RMI ?
174.What are the steps involved in RMI ?
175.What is meant by bind(), rebind(), unbind() and lookup() methods
176.What are the advanatages of RMI ?
177.What is JNI ?
178.What is Remote Interface ?
179.What class is used to create Server side object ?
180.What class is used to bind the server object with RMI Registry ?
181.What is the use of getWriter method ?
182.What is meant by Javabeans ?
183.What is JAR file ?
184.What is meant by manifest files ?
185.What is Introspection ?
186.What are the steps involved to create a bean ?
187.Say any two properties in Beans ?
188.What is persistence ?
189.What is the use of beaninfo ?
190.What are the interfaces you used in Beans ?
191.What are the classes you used in Beans ?