java - 不能将可比对象与父子孙子继承

给出以下代码:

public abstract class Participant {
    private String fullName;

    public Participant(String newFullName) {
        this.fullName = new String(newFullName);
    }

    // some more code
}


public class Player extends Participant implements Comparable <Player> {
    private int scoredGoals;

    public Player(String newFullName, int scored) {
        super(newFullName);
        this.scoredGoals = scored;
    }

    public int compareTo (Player otherPlayer) {
        Integer _scoredGoals = new Integer(this.scoredGoals);
        return _scoredGoals.compareTo(otherPlayer.getPlayerGoals());
    }

    // more irrelevant code
}

public class Goalkeeper extends Player implements Comparable <Goalkeeper> {
    private int missedGoals;

    public Goalkeeper(String newFullName) {
        super(newFullName,0);
        missedGoals = 0;
    }

    public int compareTo (Goalkeeper otherGoalkeeper) {
        Integer _missedGoals = new Integer(this.missedGoals);
        return _missedGoals.compareTo(otherGoalkeeper.getMissedGoals());
    }

    // more code
}

问题是Goalkeeper不符合要求。

当我尝试编译该代码时，Eclipse抛出:

The interface Comparable cannot be implemented more than once with
different arguments: Comparable<Player> and Comparable<Goalkeeper>

我不是要与Player进行比较，而是与Goalkeeper进行比较，并且仅与他进行比较。

我究竟做错了什么 ？

最佳答案

就设计逻辑而言，您没有做错任何事情。但是，由于Java实现泛型的方式(通过类型擦除)，Java的局限性使您无法使用不同的类型参数来实现相同的泛型接口(interface)。

在您的代码中，Goalkeeper从Player继承了Comparable <Player>的实现，并尝试添加自己的Comparable <Goalkeeper>。这是不允许的。

解决此限制的最简单方法是在Comparable <Player>中覆盖Goalkeeper，将传入的播放器转换为Goalkeeper，然后将其与this守门员进行比较。

编辑

public int compareTo (Player otherPlayer) {
    Goalkeeper otherGoalkeeper = (Goalkeeper)otherPlayer;
    Integer _missedGoals = new Integer(this.missedGoals);
    return _missedGoals.compareTo(otherGoalkeeper.getMissedGoals());
}