java - 设置: Prevent insertion of same type

Question

如果已存在相同类型的对象，我想阻止在 Set 中插入对象。示例:

如果我有以下类(class):

public class Card{...}
public class Clubs extends Card{...}
public class Diamonds extends Card{...}
public class Hearts extends Card{...}
public class Spades extends Card{...}

行为应该是:

Set<Card> cards = new HashSet<>();
System.out.println(cards.add(new Diamonds()) //prints "true"
System.out.println(cards.add(new Spades()) //prints "true"
System.out.println(cards.add(new Spades()) //prints "false"

是否有一种简单的方法或一组实现可以给我这种行为？

我考虑过为扩展 Card 的每个类重写 hashcode/equals 来管理哈希集行为，但我认为这不是一个可靠的解决方案。

编辑:

我以一张基本的牌为例，但每张牌不仅仅是一种“颜色”，字段的数量、字段的类型和每个类(梅花、方 block 、黑桃、红心)的方法都不同。

编辑2

这是我的 Card 类的更具体定义:

public abstract class Card
{
    /**Keyword of this card*/
    private final String keyword;

    public Card(String keyword)
    {
         this.keyword = keyword; 
    }

    public abstract void cardDefinition();
    ...
}

这里是我的类扩展卡的定义:

public class Diamonds extends Card
{
    /**KEYWORD of this card*/
    public static final String KEYWORD = "cell";
    /**Name of this cell*/
    private final int id;
    /**Universe of this cell*/
    private final Universe universe;
    /**Material name of this cell*/
    private final String materialName;

    public Diamonds(int id, Universe universe, String materialName)
    {
        super(KEYWORD);
        this.id = id;
        this.universe = universe;
        this.materialName = materialName;
        ...
    }
    @Override
    public void cardDefinition(){...}
    public void someMethod(OrientedSurface orientedSurface) {...}
    ...
}


public class Spades extends Card
{
    /**keyword of this card*/
    public static final String KEYWORD = "mat";
    /**Name of this material card*/
    private final String name;
    /**Density of this material card*/
    private final double density;'

    public Spades(String name, double density)
    {
        super(KEYWORD);
        this.name = name;
        this.density = density;
        ...
    }
    @Override
    public void cardDefinition(){...}
    public void someMethodBis(Material material) {...}
    ...
}
...

Answer 1

根据您更新的答案，也许使用关键字到卡片的映射可能适合您:

Map<String, Card> cards = new HashMap<>();

这是假设关键字是唯一的，并且每个关键字只能在 map 中出现一张卡片。在 map 中存储数据可能如下所示:

Card mySpade = new Spade(...);

if (!cards.contains(Spades.KEYWORD)) {
    cards.put(Spades.KEYWORD, mySpade);
}...