Is it possible to monkey patch in Java?

Question

I don\'t want to discuss the merits of this approach, just if it is possible. I believe the answer to be \"no\". But maybe someone will surprise me!

Imagine you have

Answer 1

The object-oriented way of doing this would be to create a wrapper implementing IWidget, delegating all calls to the actual widget, except calculateHeight, something like:

class MyWidget implements IWidget {
    private IWidget delegate;
    public MyWidget(IWidget d) {
        this.delegate = d;
    }
    public int calculateHeight() {
        // my implementation of calculate height
    }
    // for all other methods: {
    public Object foo(Object bar) {
        return delegate.foo(bar);
    }
}

For this to work, you need to intercept all creations of the widget you want to replace, which probably means creating a similar wrapper for the WidgetFactory. And you must be able to configure which WidgetFactory to use.

It also depends on no client trying to cast the IWidget back to DefaultWidget...