java - 从包含自定义类的 ArrayList 中删除重复元素

Question

我有一个自定义类Highscore的ArrayList数组列表包含多个 Highscore

如下面的代码所示，存在重复条目。也就是说， highscores.add(new Highscore("user 1", 25)); 当我说重复时，我指的是相同的 String (用户名)和 int(分数)值

我希望能够检测到它，以便只有其中 1 个条目保留在 ArrayList

代码:

ArrayList<Highscore> highscores = new ArrayList<>();
highscores.add(new Highscore("user 1", 25));
highscores.add(new Highscore("user 2", 10));
highscores.add(new Highscore("user 3", 55));
highscores.add(new Highscore("user 1", 25));
highscores.add(new Highscore("user 2", 5));
highscores.add(new Highscore("user 3", 30));

高分:

public class Highscore implements ConfigurationSerializable {

    String username;
    public int score;

    public Highscore(String username, int score) {
        this.username = username;
        this.score = score;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public int getScore() {
        return score;
    }

    public void setScore(int score) {
        this.score = score;
    }

    @Override
    public Map<String, Object> serialize() {
        Map<String, Object> mappedObject = new LinkedHashMap<String, Object>();
        mappedObject.put("username", username);
        mappedObject.put("score", score);
        return mappedObject;
    }

    public static Highscore deserialize(Map<String, Object> mappedObject) {
        return new Highscore((String) mappedObject.get("username"),
                (int) mappedObject.get("score"));
    }
}

我看到有些人建议使用 HashSet 或 LinkedHashSet，但就我而言，这不起作用，因为它根据 Highscore 的 ID 来识别重复项，而该 ID 总是不同的。

提前致谢:)

Answer 1

I have seen some people suggest using a HashSet or LinkedHashSet, but in my case, that doesn't work as it identifies duplicates based on the id of the Highscore, which is always different.

您可以通过重写equals(和hashCode)方法来定义“相似”的含义。有关详细说明，请参阅this .

如果您的要求是不允许基于您的类的属性出现重复 - Set是一个不错的选择。例如HashSet 。您必须重写 equals 和 hashCode 方法:

class Highscore {

    private String username;
    public int score;

    //getters setters constructors

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Highscore highscore = (Highscore) o;
        return score == highscore.score &&
                Objects.equals(username, highscore.username);
    }

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

然后:

Set<Highscore> highscores = new HashSet<>();

highscores.add(new Highscore("user 1", 25));
highscores.add(new Highscore("user 2", 10));
highscores.add(new Highscore("user 3", 55));
highscores.add(new Highscore("user 1", 25));
highscores.add(new Highscore("user 2", 5));
highscores.add(new Highscore("user 3", 30));

System.out.println(highscores.size());

将打印5并且不添加重复条目。如果您想保留插入顺序，请使用 LinkedHashSet .

当然，您也可以使用 ArrayList 并通过调用 List::remove(object) 来删除元素但它也使用 equals 来比较下面的对象。我认为这里使用 Set 是可取的。