Question

I’m currently experimenting with decorators. I created a Tank class and two decorators: DoubleGunTank (shoots more powerfully) and FasterTank (drives faster). Here they are:

public class Tank {
    public int shoot() {
        return 100;
    }

    public int drive() {
        return 10;
    }
}
public class FasterTank extends Tank {

    protected Tank fTank;

    public FasterTank(Tank tank) {
        fTank = tank;
    }

    public int drive() {
        return fTank.drive() * 2;
    }
}

public class DoubleGunTank extends Tank {

    protected Tank fTank;

    public DoubleGunTank(Tank tank) {
        fTank = tank;
    }
    public int shoot() {
        return fTank.shoot() * 2;
    }   
}

What I’m trying to do is decorate one tank with both double gun and the super speed. So I do it like this:

Tank czolg = new Tank();
czolg = new FasterTank(czolg);
czolg = new DoubleGunTank(czolg);
System.out.println("Shoot: "+czolg.shoot());
System.out.println("Drive: "+czolg.drive());

But the result is:

Shoot: 200
Drive: 10

It seems that only one decorator activates both methods from the DoubleGunTank class. So my question is: how do I get the tank to shoot more powerfully and drive faster at the same time?

Answer 1

Not quite sure about the Decorator pattern but czlog.drive() invokes Tank.drive() because DoubleGunTank does not override it.

You need to override every method in the superclass and delegate it to the contained fTank for this to work like you want it to.