使用比较器将列表添加到树集

Question

因此，我必须创建一个分数高于给定分数的播放器对象的TreeSet。 我不允许使用任何形式的for循环。 我已经编写了一个比较器并创建了Need对象的列表，但是当我将列表添加到树集时，我得到一个Player不能转换为java.lang.Comparable错误。

注意：一切正常，直到我尝试将其添加到树集中，如果我将树集取出并只打印highPlayers，它就会给我我想要的列表。

为什么不让我将此列表添加到树集？ 谢谢

public class TreeSetProblems2 {

    public static void main(String[] args) {
        List<Player> players = new ArrayList<>();

        Player p1 = new Player("Tom", 3);
        Player p2 = new Player("Bucky", 42);
        Player p3 = new Player("Tina", 23);
        Player p4 = new Player("Bob", 15);
        Player p5 = new Player("Shaun", 2);
        //Player p6 = new Player("Tommy", 3);

        players.add(p1);
        players.add(p2);
        players.add(p3);
        players.add(p4);
        players.add(p5);

        System.out.print(highRollers(players, 9));
    }

    public static TreeSet<Player> highRollers(List<Player> players, int score){
        TreeSet<Player> treeplayers = new TreeSet<>();
        Player dummy = new Player("Dummy", score);
        players.add(dummy);
        ScoreComparator sc = new ScoreComparator();
        Collections.sort(players, sc);
        int index = players.indexOf(dummy);
        List<Player> highPlayers = players.subList(index+1, players.size());
        treeplayers.addAll(highPlayers);
        return treeplayers;
    }


} 

Answer 1

我发现了自己的解决方案：

public static TreeSet<Player> highRollers(List<Player> players, int score) {
    TreeSet<Player> treeplayers = new TreeSet<>(new ScoreComparator());
    treeplayers.addAll(players);

    while(treeplayers.first().getScore() < score) {
        treeplayers.pollFirst();
    }

    return treeplayers;
}

甚至更简单：

public static TreeSet<Player> highRollers(List<Player> players, int score) {
    TreeSet<Player> treeplayers = new TreeSet<>(new ScoreComparator());
    TreeSet<Player> highRollers = new TreeSet<>(new ScoreComparator());

    treeplayers.addAll(players);
    highRollers.addAll(treeplayers.tailSet(new Player("Dummy", score)));

    return highRollers;
}

Answer 2

关键点似乎是TreeSet只能包含实现Comparable接口的类的元素。 您必须更改“ Player”类才能这样做。