如何以相同的方式覆盖多个类中父级的方法，而不在父子级之间创建 class？

Question

It's hard to properly ask, so I will create an example:

class Animal {

    public void doSomething() {
    }
}

class Dog extends Animal {

}

class Cat extends Animal {

}

class Sheltie extends Dog {

    @Override
    public void doSomething() {
        super.doSomething();
        System.out.println("Exactly the same");
    }
}

class Abbysian extends Cat {

    @Override
    public void doSomething() {
        super.doSomething();
        System.out.println("Exactly the same");
    }
}

Is there a way in this case that I can override the doSomething() method in both Sheltie and Abbysian without duplicating a code and even typing @Override public void doSomething() . On top of that, I'd actually like to call super.doSomething() as well. I cannot change inheritance at all.

If those classes extended directly Animal I would create a class "between" them. I was thinking of using interface with default method but that didn't help as well.

Answer 1

Once you broke out into Cats and Dogs you discovered the limitations of class hierarchy - eventually you'll hit a point of no return.

Thankfully there is a thing called an Entity Component System (ECS) that is commonly used when you want to mish-mash functionality amongst many different entities.

A cat can wag its tail. A dog can wag its tail... but not all animals have tails. So you register a component called Tail to the tailed animal entities.

I found this on the StackExchange code review group. https://codereview.stackexchange.com/questions/163215/entity-component-system-ecs

Answer 2

Decorator pattern can do this trick but it would be applied to specific instances of Sheltie / Abyssinian not to these classes:

class AnimalDecorator extends Animal {
    protected Animal animal;

    public AnimalDecorator(Animal animal) {
        this.animal = animal;
    }

    @Override
    public void doSomething() {
        animal.doSomething(); // instead of call to super.doSomething
        System.out.println("Exactly the same");
    }
}

class Sheltie extends Dog { // doSomething not overridden
}

class Abyssinian extends Cat { // doSomething not overridden
}

// decorated instances
Animal sheltie = new AnimalDecorator(new Sheltie());
Animal abyssinian = new AnimalDecorator(new Abyssinian());
sheltie.doSomething();
abyssinian.doSomething();