Interface Example

Objects.java

public interface MovableObject {
    void move();
}

public abstract class Animal implements MovableObject {
    abstract public void walk();
}

public class Human extends Animal {
    @Override
    public void walk() {
        System.out.println("Human walks using their legs.");
    }
    @Override
    public void move() {
        walk();
    }
}

public abstract class Car implements MovableObject {
    abstract public void drive();
}

public class Ford extends Car {
    @Override
    public void drive() {
        System.out.println("Ford drives with an engine.");
    }
    @Override
    public void move() {
        drive();
    }
}

VirtualWorld.java

class World {
    public static void main(String args[]) {
        ArrayList<MovableObject> objs = new ArrayList<MovableObject>();
        objs.add(new Human());
        objs.add(new Ford());
        for (MovableObject obj : objs) {
            obj.move();
        }
    }
}