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Java Interview Questions and Answers


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 accommodate platform-specific differences among windowing systems.

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.

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

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.

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.

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.

Can an exception be rethrown?
Yes, an exception can be rethrown.

Which Math method is used to calculate the absolute value of a number?
The abs() method is used to calculate absolute values.

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.

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.

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.

Which class is the immediate superclass of the Container class?
Component

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.

How can the Checkbox class be used to create a radio button?
By associating Checkbox objects with a CheckboxGroup.

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

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

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.

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

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