Override a function without extending the class

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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. java share|improve this question edited Aug 14 '12 at 0:35 asked Aug 13 '12 at 6:33 Tran Son Hai 987726

why not a method2? –  Senthil Kumar Aug 13 '12 at 6:34 add comment

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up vote43down voteaccepted	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. share|improve this answer answered Aug 13 '12 at 6:35 jensgram 17k13755
	13   True, however technically this is creating an anonymous class that extends the class A. –  Stephen C Aug 13 '12 at 6:37 @StephenC Indeed. I have updated the answer. Thanks for pointing out. –  jensgram Aug 13 '12 at 6:38 @jensgram This might be late but thank you very much. –  Tran Son Hai Mar 16 '13 at 23:25 add comment

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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 closure, which should come along with next release 8 of Java SE.