java - 在 getter 方法中返回子类而不知道子类

Question

我有一个抽象类Item子类为 Weapon 的类Shield和Potion 。

abstract public class Character {

    private Item item;

    public Character(Item item) {
        this.item = item;
    }

    public Item getItem() {
        return this.item;
    }
}

public class Hero extends Character{

    public Hero(Item item) {
        super(item);
    }
    public static void main(String[] args) {
        Hero h = new Hero(new Weapon("sword"));
        System.out.println(h.getItem().getDamage());
        /* getDamage is not known because it is not a method of the Item
           class, it is a method of the Weapon class */

        Hero h1 = new Hero(new Potion("syrup"));
        System.out.println(h1.getItem().getPower());
        /* again getPower() is not known */
    }
}

我该怎么做才能this.item返回为 Weapon/Potion...而不是 Item 。我做了研究，发现我需要改变方法public Item getItem()方法public <T extends Item> getItem()或投 this.item作为Weapon/Potion/Shield但我不知道该怎么做。

Answer 1

abstract class Character
{
    private Item item;

    public Character (Item item)
    {
        this.item = item;
    }

    public <T extends Item> T getItem (Class <? extends T> targetType)
    {
        return targetType.cast(this.item);
    }

    public void setItem (Item item)
    {
        this.item = item;
    }
}

class Hero extends Character
{
    public Hero (Item item)
    {
        super (item);
    }

    public static void main(String[] args) {

        Hero hero1 = new Hero(new Weapon("sword"));
        Weapon weapon = hero1.getItem(Weapon.class);
        hero1.setItem(new Potion("syrup"));
        Potion potion = hero1.getItem(Potion.class);
    }
}