Downcasting in Java

Question

Upcasting is allowed in Java, however downcasting gives a compile error.

The compile error can be removed by adding a cast but would anyway break at the runtime.

Answer 1

Using your example, you could do:

public void doit(A a) {
    if(a instanceof B) {
        // needs to cast to B to access draw2 which isn't present in A
        // note that this is probably not a good OO-design, but that would
        // be out-of-scope for this discussion :)
        ((B)a).draw2();
    }
    a.draw();
}