Java Extending Final Classes

Question

I would like to override a 3rd party, open-source final class's non-final method.

final class A 
{
    void put(obj a)
    {...}

    obj get()
    {...}
}

Please tell me how to override the get() and put() methods, yet still retain the other behaviour and functionality of this class.

Answer 1

It's open source: fork it, and make the class non-final.

You won't be able to extend it without making it non-final.

Answer 2

If your class has a defined interface in which put and get methods are defined then You may want to try to proxy the class.

The easiest way is to create something like this:

public interface CommonInterface {

void put(); Object get();

}

final class A implements CommonInterface
{

void put(obj a)
{...}
obj get()
{...}

}

public class ProxyToA implements CommonInterface{

   private A a;

  void put(Object a){
   // your override functionality

  } 

    Object get(){
       // same here
    }

   void otherAStuff(){
        a.otherAStuff();
   }

}

And then just use CommonInterface and proxy your object. Or you can use JDK proxies, javassist, etc.