Question

我不知道为什么我的列表没有排序。

我使用Collection.sort，它似乎可以完成这项工作，但是当我启动UnitTest时，它会输出错误。

预期：characterWithMaxVotes [voteCount：100]

实际：characterMiddle75 [voteCount：75]

//Exact same method as in the Character class (pasted for better readability on SO question)
public static void sortCharactersByVotes(List<Character> lstCharacters) {
    Collections.sort(lstCharacters, new Comparator<Character>() {
        @Override
        public int compare(Character character, Character p1) {
            int result = (character.getVoteCount() > p1.getVoteCount()) ? 1 : 0;
            return result;
        }
    });
}

@Test
public void sortCharactersByVoteCounts() {
    Character characterWithMinVotes = Character.newBuilder().name("characterWithMinVotes").voteCount(0).build();
    Character characterMiddle25 = Character.newBuilder().name("characterMiddle25").voteCount(25).build();
    Character characterMiddle75 = Character.newBuilder().name("characterMiddle75").voteCount(75).build();
    Character characterWithMaxVotes = Character.newBuilder().name("characterWithMaxVotes").voteCount(100).build();

    List<Character> lstCharacters = new ArrayList<>();

    lstCharacters.add(characterMiddle75);
    lstCharacters.add(characterWithMaxVotes );
    lstCharacters.add(characterMiddle25);
    lstCharacters.add(characterWithMinVotes);

    sortCharactersByVotes(lstCharacters);

    System.out.print(lstCharacters);

    assertEquals(lstCharacters.get(0), characterWithMaxVotes);
    assertEquals(lstCharacters.get(1), characterMiddle75);
    assertEquals(lstCharacters.get(2), characterMiddle25);
    assertEquals(lstCharacters.get(3), characterWithMinVotes);
}

如何正确地做到这一点，谢谢你的帮助。

PS：根据要求，这是我的角色类

公共类字符{

private static final String TAG = "Character";

private int id;
private String name = "";
public int voteCount;
public boolean isVotedByUser = false;

public int getId() {
    return id;
}
public int getVoteCount() {
    return voteCount;
}
public String getName() {
    return name;
}

public static CharacterBuilder newBuilder(){
    return new CharacterBuilder();
}

@Override
public String toString() {
    return name + "[voteCount : " + voteCount + "]";
}

public static void sortCharactersByVotes(List<Character> lstCharacters) {
    Collections.sort(lstCharacters, new Comparator<Character>() {
        @Override
        public int compare(Character character, Character p1) {
            int result = (character.getVoteCount() > p1.getVoteCount()) ? 1 : 0;
            return result;
        }
    });
}

public static class CharacterBuilder {

    public Character character;

    CharacterBuilder() {
        character = new Character();
    }

    public CharacterBuilder id(int id) {
        character.id = id;
        return this;
    }

    public CharacterBuilder name(String name) {
        character.name = name;
        return this;
    }

    public CharacterBuilder voteCount(int voteCount) {
        character.voteCount = voteCount;
        return this;
    }

    public Character build() {
        return character;
    }

}

}

Answer 1

（根据建议编辑使用Integer.compare）

当且仅当两个比较的对象具有相等的＆＃34; rank＆＃34; （在您的情况下，等于投票数）时，compare方法必须返回0，否则必须如果a> b则返回正值;如果b> a，则返回负值（反之亦然，根据所需的排序方向）。

要简单地解决这个问题，你可以写（假设getVoteCount()是int）：

public int compare(Character character, Character p1) { return Integer.compare(p1.getVoteCount(), character.getVoteCount()); }

（反转排序结果，只需交换操作数）

Answer 2

Comparator的实施方式不正确，因为您希望首先获得最高价值（而不是首先具有相反的最低值），如果character.getVoteCount() < p1.getVoteCount()和character.getVoteCount() > p1.getVoteCount()，您应该返回正值如果getVoteCount()为负值，则应使用Integer.compare(int x, int y)来比较int的值（假设它返回Comparator），以便new Comparator<Character>() { @Override public int compare(Character c1, Character c2) { return Integer.compare(c2.getVoteCount(), c1.getVoteCount()); } }可以是：

getVoteCount()

NB：不要将window的值与简单的减法进行比较，否则您将冒险获得不正确的结果，因为它容易出现溢出问题。

Answer 3

我认为更好地改变比较器实现的一点点。尝试：

name

另一件事是你要加两次

<强> characterWithMaxVotes

希望它有所帮助！

Answer 4

您的比较方法应修改为

public static void sortCharactersByVotes(List<Character> lstCharacters) {
    lstCharacters.sort(Comparator.comparingInt(Character::getVoteCount));
}

注意 - 比较基于getVoteCount的整数Character， Java 8 +

排序集合未按预期工作

4 个答案: