Override a function without extending the class

Question

Suppose I have a class A:

public class A {     public A(){....}     public void method1() {...} }; 

And an instance of that class:

A anA = new A(); 

Is there any way to override the method1() only for anA? This question arises when I write a small painting program in which I have to extend the JPanel class several times just to make minor changes to the different panels that have slightly different characteristics.

Answer 1

You can do the following:

A anA = new A() {     public void method1() {         ...     } }; 

This is the same as:

private static class myA extends A {     public void method1() {         ...     } }  A anA = new myA(); 

Only with the exception that in this case myA can be reused. That's not possible with anonymous classes.

Answer 2

You can create a an new anonymous class on the fly, as long as you are using the no-arg constructor of your class A:

A anA = new A() {    @Override   public void method1() {     ...   } }; 

Note that what you want to do is very close to what is known as a lambda, which should come along the next release 8 of Java SE.