Equivalent to extending a final class in Java

Question

I know that in Java we can't extend a final class. But is there any alternative way where I get the effect of extending a final class?

Because I have a final class with the requirements I am looking for, so if somehow I can reuse this, it would be of great help for me.

Answer 1

Create a wrapper for the final class?

Something like this:

class MyClass {
    private FinalClass finalClass;

    public MyClass {
        finalClass = new FinalClass():
    }

    public void delegatingMethod() {
        finalClass.delegatingMethod();
    }
}

A wrapper class like MyClass won't be accepted as an instance of FinalClass. If FinalClass implements any interfaces you can implement them in MyClass to make the classes more alike. The same is true of any non-final parents of the FinalClass; in that case your MyClass design should be compatible with those parent classes though.

It is even possible to create a wrapper class during runtime using reflection. In that case you can use the Proxy class. Beware that proxy classes do require in depth knowledge about the Java type system.

Answer 2

The simplest option would be to write a wrapper, which contains an instance of the final class as a member variable and acts as a proxy to the final class.

This way, it's easy to override or extend methods of the final class.