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Core Java Interview Question, Interview Question

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Core Java Interview Question Page 23


Question: To what value is a variable of the boolean type automatically initialized?

The default value of the boolean type is false.

Question: Can try statements be nested?

Try statements may be tested.

Question: What is the difference between the prefix and postfix forms of the ++ operator?

The prefix form performs the increment operation and returns the value ofthe 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?

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?

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?

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

Question: 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.

Question: 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.

Question: Can an unreachable object become reachable again?

Answer: 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.

Question: When is an object subject to garbage collection?

Answer: An object is subject to garbage collection when it becomes unreachable to the program in which it is used.

Question: What method must be implemented by all threads?

Answer: All tasks must implement the run() method, whether they are a subclass ofThread or implement the Runnable interface.

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

Answer: getLabel() and setLabel()

Question: Which Component subclass is used for drawing and painting?

Answer: Canvas

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 are the two basic ways in which classes that can be run as threads may be defined?

Answer: A thread class may be declared as a subclass of Thread, or it may implement the Runnable interface.

Question: What are the problems faced by Java programmers who don't use layout managers?

Answer: Without layout managers, Java programmers are faced with determining how their GUI will be displayed across multiple windowing systems and finding a common sizingand positioning that will work within the constraints imposed by each windowing system.

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 happens when you add a double value to a String?

Answer: The result is a String object.

Question: What is the List interface?

Answer: The List interface provides support for ordered collections of objects.


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