Sorry, i really dont know how to make a headline for that question; maybe there is a name for what im trying to do that i dont know, but i can explain it with some code:

Guess you have a class that unfortunately neither has a copy-constructor nor a public static copy method.

class A
{
    private int i;  // <- private, cant access
    String x;       // <- even worse: cant access unless in same pkg!
    /* … other stuff, ctor, etc. … */
    public A clone()
    {
        A a = new A();
        a.i = i;
        a.x = x;
        return x;
    }
}

Guess further, there is some function that returns an object of that class:

public static A someFn(x,y,z);

Now the problem: I want to derive from that class to add some functionality. Unfortunately, i neither have a sizeof in java nor a cc or static copy method.

So when i do a

class B extends A
{
    protected w;
    public B clone()
    {
       /* as usual */
    }
}

then i can clone my B and get a new one, but how can i convert the returned A from someFn() into a B. Is there anyway to do the opposite of slicing in java? if i clone it, it's still an A, and i cant copy it field by field. This is all simple in c++, but how to do this in Java?