Overriding a method in an instantiated Java object

Question

I would like to override a method in an object that's handed to me by a factory that I have little control over.

My specific problem is that I want to override the getInputStream and getOutputStream of a Socket object to perform wire logging.

The generic problem is as follows:

public class Foo {     public Bar doBar() {         // Some activity     } } 

Where I'd like to take an instantiated Foo and replace the doBar with my own that would work as follows:

Bar doBar() {     // My own activity     return original.doBar(); } 

For the Socket I'm going to return an InputStream and OutputStream that are wrapped by logging to intercept the data.

Answer 1

Since Java uses class-based OO, this is impossible. What you can do is use the decorator pattern, i.e. write a wrapper for the object that returns the wrapped streams.

Answer 2

I think there is a way to achieve the effect you want. I saw it orriginally used in swing with buttons to allow the programmer to make the button do something when it is clicked.

Say you have your Foo class:

public class Foo {   public Bar doBar() {     // Some activity   } } 

Then you have a runner class or something similar. You can override the doBar() method at the point of instantiation and it will only affect that specific object.

that class may look like this:

public class FooInstance{   Foo F1 = new Foo(){     public Bar doBar(){       //new activity     }   }    Foo F2 = new Foo();    F1.doBar(); //does the new activity   F2.doBar(); //does the original activity found in the class } 

I'm not entirely sure that will do the trick for you but maybe it'll set you in the right direction. If nothing else it is possible to override a method outside of the class, maybe that will help you.