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Java:如何根据属性值将对象合并到ARARYLIST中?

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Matias Diez · 技术社区 · 6 年前

我正在使用Spring Bug、Java和MySQL构建(或学习如何)一个运动REST API。我正在构建一个方法,该方法当前从匹配项集合中获取每个匹配项并返回 ArrayList 属于 TeamStandings 完整的匹配列表。

方法如下:

public List<TeamStanding> createStandingsTable(Match[] matches){
        List<TeamStanding> teamStandings = new ArrayList<TeamStanding>();
        for(int i = 0;i < matches.length; i++) {
            TeamStanding firstTeam = new TeamStanding();
            TeamStanding secondTeam = new TeamStanding();

            //set team ids
            firstTeam.setIdTeam(matches[i].getWcmHome());
            secondTeam.setIdTeam(matches[i].getWcmAway());


            //first team stats
            firstTeam.setTeamPlayed((long) 1);
            firstTeam.setTeamGoalsFavor(matches[i].getWcmHomeGoals());
            firstTeam.setTeamGoalsAgainst(matches[i].getWcmAwayGoals());
            firstTeam.setTeamGoalDif(firstTeam.getTeamGoalsFavor() - firstTeam.getTeamGoalsAgainst());

            //second team stats
            secondTeam.setTeamPlayed((long) 1);
            secondTeam.setTeamGoalsFavor(matches[i].getWcmAwayGoals());
            secondTeam.setTeamGoalsAgainst(matches[i].getWcmHomeGoals());
            secondTeam.setTeamGoalDif(secondTeam.getTeamGoalsFavor() - secondTeam.getTeamGoalsAgainst());

            //combined team stats

            if(firstTeam.getTeamGoalsFavor() > secondTeam.getTeamGoalsFavor()) {
                firstTeam.setTeamWins((long) 1);
                firstTeam.setTeamLoses((long) 0);
                firstTeam.setTeamDraws((long) 0);
                firstTeam.setTeamPoints((long) 3);
                secondTeam.setTeamWins((long) 0);
                secondTeam.setTeamLoses((long) 1);
                secondTeam.setTeamDraws((long) 0);
                secondTeam.setTeamPoints((long) 0);
            } else if (firstTeam.getTeamGoalsFavor() == secondTeam.getTeamGoalsFavor()) {
                firstTeam.setTeamWins((long) 0);
                firstTeam.setTeamLoses((long) 0);
                firstTeam.setTeamDraws((long) 1);
                firstTeam.setTeamPoints((long) 1);
                secondTeam.setTeamWins((long) 0);
                secondTeam.setTeamLoses((long) 0);
                secondTeam.setTeamDraws((long) 1);
                secondTeam.setTeamPoints((long) 1);
            } else {
                firstTeam.setTeamWins((long) 0);
                firstTeam.setTeamLoses((long) 1);
                firstTeam.setTeamDraws((long) 0);
                firstTeam.setTeamPoints((long) 0);
                secondTeam.setTeamWins((long) 1);
                secondTeam.setTeamLoses((long) 0);
                secondTeam.setTeamDraws((long) 0);
                secondTeam.setTeamPoints((long) 3);
            }
            teamStandings.add(firstTeam);
            teamStandings.add(secondTeam);
        }
        return teamStandings;
    }

结果是这样的:

[
    {
        "idTeam": 7,
        "teamPoints": 3,
        "teamPlayed": 1,
        "teamWins": 1,
        "teamDraws": 0,
        "teamLoses": 0,
        "teamGoalsFavor": 4,
        "teamGoalsAgainst": 1,
        "teamGoalDif": 3
    },
    {
        "idTeam": 13,
        "teamPoints": 0,
        "teamPlayed": 1,
        "teamWins": 0,
        "teamDraws": 0,
        "teamLoses": 1,
        "teamGoalsFavor": 1,
        "teamGoalsAgainst": 4,
        "teamGoalDif": -3
    },
    {
        "idTeam": 4,
        "teamPoints": 3,
        "teamPlayed": 1,
        "teamWins": 1,
        "teamDraws": 0,
        "teamLoses": 0,
        "teamGoalsFavor": 1,
        "teamGoalsAgainst": 0,
        "teamGoalDif": 1
    },
    {
        "idTeam": 7,
        "teamPoints": 0,
        "teamPlayed": 1,
        "teamWins": 0,
        "teamDraws": 0,
        "teamLoses": 1,
        "teamGoalsFavor": 0,
        "teamGoalsAgainst": 1,
        "teamGoalDif": -1
    }
]

我的问题是如何根据 idTeam

[
        {
            "idTeam": 7,
            "teamPoints": 3,
            "teamPlayed": 2,
            "teamWins": 1,
            "teamDraws": 0,
            "teamLoses": 1,
            "teamGoalsFavor": 4,
            "teamGoalsAgainst": 2,
            "teamGoalDif": 2
        },
        {
            "idTeam": 13,
            "teamPoints": 0,
            "teamPlayed": 1,
            "teamWins": 0,
            "teamDraws": 0,
            "teamLoses": 1,
            "teamGoalsFavor": 1,
            "teamGoalsAgainst": 4,
            "teamGoalDif": -3
        },
        {
            "idTeam": 4,
            "teamPoints": 3,
            "teamPlayed": 1,
            "teamWins": 1,
            "teamDraws": 0,
            "teamLoses": 0,
            "teamGoalsFavor": 1,
            "teamGoalsAgainst": 0,
            "teamGoalDif": 1
        }
    ]

3 回复 | 直到 6 年前

Nikolas Charalambidis 6 年前

遍历 TeamStanding 注意团队ID并执行添加。您可能希望使用映射将团队ID对保存为键,并将团队本身保存为值,以便于操作。这是截图(我还没有测试过,所以你可能需要修改一下)。

List<TeamStanding> list = createStandingsTable(matches);
Map<Integer, TeamStanding> map = new HashMap<>();

for (TeamStanding team: list) {
    int id = team.getIdTeam();
    if (map.containsKey(id)) {
        TeamStanding other = map.get(id);
        other.setTeamPoints(team.getTeamPoints());
        other.setTeamPlayed(team.getTeamPlayed());
        // and so on...
    } else {
        map.put(id, team);
    }
}

List<TeamStanding> merged = new ArrayList<>(map.values());

如果要创建合并的 List<TeamStanding> 直接来自 Match[] ,然后您必须使用相同的思想,但是,将两个迭代组合在一起可能有点复杂。然后我建议您坚持这两个独立的迭代。与性能相比,简洁性、可读性和可维护性——此外,性能并不是真正的问题。

Arun Chaudhary 6 年前

您可以使用hashmap。使用“idteam”作为键,对象teamstanding作为值。现在您可以迭代结果列表,如果您在映射中找到了对象,只需更新其字段,如果没有找到,则插入对象。迭代完成后,可以调用map.values(),它将为您提供一个对象集合(teamstanding),然后可以使用该集合创建一个新的arraylist。

代码如下:

public List<TeamStanding> mergeTeamStandingList(List<TeamStanding> teamStandingList) {
    final Map<Integer, TeamStanding> idTeamVsTeamStandingMap = new HashMap<Integer, TeamStanding>();
    teamStandingList.forEach(teamStanding -> {
        if(idTeamVsTeamStandingMap.containsKey(teamStanding.getIdTeam())) {
            TeamStanding teamStanding1 = idTeamVsTeamStandingMap.get(teamStanding.getIdTeam());
            teamStanding1.setTeamDraws(teamStanding1.getTeamDraws() + teamStanding.getTeamDraws());
            //so on
        } else {
            idTeamVsTeamStandingMap.put(teamStanding.getIdTeam(), teamStanding);
        }
    });

    return new ArrayList<>(idTeamVsTeamStandingMap.values());
}

Nico Van Belle 6 年前

在您的 Teamstanding

public TeamStanding merge(TeamStanding other) {
     this.teamPoints += other.getTeamPoints();
     this.teamPlayed += other.getTeamPlayed();
     this.teamWins += other.getTeamWins();
     this.teamDraws += other.getTeamDraws();
     this.teamGoalsFavor += other.getTeamGoalsFavor();
     this.teamLoses += other.getTeamLoses();
     this.teamGoalDif += other.getTeamGoalDif();
     return this;
}

Map<Integer, Optional<TeamStanding>> mapReduced = teamStandings
.stream()
.collect(groupingBy(TeamStanding::getIdTeam, Collectors.reducing(TeamStanding::merge)));