core java interview questions and answers for freshers pdf free download

Core Java Interview Questions-->5

181) What happens when you add a double value to a String?

The result is a String object.

182) 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..

183) Which package is always imported by default?

The java.lang package is always imported by default.

184) 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.

185) 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.

186) 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.

187) What is a compilation unit?

A compilation unit is a Java source code file.

188) What interface is extended by AWT event listeners?

All AWT event listeners extend the java.util.EventListener interface.

189) 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 thrownby the overridden method.

190) How can a dead thread be restarted?

A dead thread cannot be restarted.

191) 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.

192) What is a layout manager?

A layout manager is an object that is used to organize components in a container.

193) Which arithmetic operations can result in the throwing of an ArithmeticException?

Integer / and % can result in the throwing of an ArithmeticException.

194) 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.

195) Can an abstract class be final?

An abstract class may not be declared as final.

196) 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.

197) 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.

198) 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.

199) 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.

200) What is the difference between a public and a nonpublic class?

A public class may be accessed outside of its package. A non-public class may not be accessed outside of its package.

201) To what value is a variable of the boolean type automatically initialized?

The default value of the boolean type is false.

202) Can try statements be nested?

Try statements may be tested.

203) 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.

204) What is the purpose of a statement block?

A statement block is used to organize a sequence of statements as a single statement group.

205) 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.

206) What modifiers may be used with a top-level class?

A top-level class may be public, abstract, or final.

207) 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..

208) 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.

209) 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.

210) 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.

211) 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.

212) What methods are used to get and set the text label displayed by a Button object?

getLabel() and setLabel()

213) Which Component subclass is used for drawing and painting?

Canvas

214) 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.

215) 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.

216) 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.

217) 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.

218) What happens when you add a double value to a String?

The result is a String object.

219) What is the List interface?

The List interface provides support for ordered collections of objects.