如何比较类对象？[副本]

Question

我想比较两个物体。然而，当我运行它时，它告诉我它们不匹配，尽管它们匹配。请让我知道我做错了什么，谢谢。下面是我的代码：

      Player p1 = new Player("Mo", "Food", 200.0,0.0);
      Player p2 = new Player("Mo", "Food", 200.0,0.0);
      
      System.out.println(p1.equals(p2)); // -- false

Answer 1

您的equals()正在调用默认的对象类的方法，该方法比较对象的标识^*，即p1==p2，而不是其内容。这是来自对象的默认equals:

public boolean equals(Object obj) {
    return (this == obj);
}

如果要定义逻辑以确定两个播放器是否相等，则需要重写：

• equals()方法
• hashcode()实现equals-hash协定的方法

class Player {
    private String firstName;
    private String lastName;
    private double score;
    private double rating;

    // ...

    @Override
    public int hashCode() {
        return Objects.hash(firstName, lastName, score, rating);
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null || getClass() != obj.getClass())
            return false;
        Player other = (Player) obj;
        return Objects.equals(firstName, other.firstName) && Objects.equals(lastName, other.lastName)
                && score == other.score && rating == other.rating;
    }

    // ...
}

record Point(String firstName, String lastName, double score, double rating) { }

null

class Player implements Comparable<Player> 
{
   @Override
   public int compareTo(Player p2)  
   {
      /* Allows returning : (0)-> this==p2 | (1)-> this>p2 | (-1)-> this<p2
        Anyway, the meaning of 1 and -1 is up to you.
        if (this.name.equals(p2.name) && ...)
           return 0;
       else if ... 
            return 1;
       return -1;     */
   }
}