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April 9, 2016 Categories: Event Handling. No Comments on Inner Classes

In this article we will learn about inner classes and how can they be used to simplify event handling process along with sample Java programs.


An inner class is a class which is defined inside another class. The inner class can access all the members of an outer class, but vice-versa is not true. The mouse event handling program which was simplified using adapter classes can further be simplified using inner classes.


Following is a Java program which handles the mouse click event using inner class and adapter class:



In the above example, the class MyAdapter is the inner class which has been declared inside the outer class MyApplet.


Anonymous Inner Classes


Anonymous inner classes are nameless inner classes which can be declared inside another class or as an expression inside a method definition.


The above mouse event handling program can further be simplified by using an anonymous inner class as shown below:



In the above program, the syntax¬†new MouseAdapter() {…} says to the compiler that the code written in between the braces represents an anonymous inner class and it extends the class MouseAdapter.


Whenever the line addMouseListener… executes, Java run-time system automatically creates the instance of anonymous inner class.

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