使用组合而不是继承时，数组应该存储什么类型？

Question

使用继承时，您可以创建两个继承自类

A

的类

B

和

C

。然后，您可以创建一个

C

数组来存储其中任意一个 -

C[]

。

但是，当使用组合时，数组必须是什么类型才能存储这两种类型？

class Entity {
    public int id;

    public Entity() {
        this.id = 0;
    }
}

class Player extends Entity {
    public Player() {
        this.id = 1;
    }
}

class Monster extends Entity {
    public Monster() {
        this.id = 2;
    }
}

public class Main {
    public static void main(String[] args) {
        Entity[] entities = new Entity[2];
 
        entities[0] = new Player(); // id == 1
        entities[1] = new Monster(); // id == 2
    }
}

使用组合时，您必须将实体存储为字段：

class Entity {
    public int id;

    public Entity() {
        this.id = 0;
    }
}

class Player {
    Entity entity;

    public Player() {
        this.entity = new Entity();
        this.entity.id = 1;
    }
}

class Monster {
    Entity entity;

    public Monster() {        
        this.entity = new Entity();
        this.entity.id = 2;
    }
}

public class Main {
    public static void main(String[] args) {
        Player player = new Player();
        Monster monster = new Monster();
        
        Entity[] entities = new Entity[2];
        // TODO: won't work! what type?
        entities[0] = player;
        entities[1] = monster;
    }
}

Answer 1

这里只能存储实体。所以只需添加player.entity/monster.entity或其他什么。