如何比较保存在ArrayList中的对象中的字符串，然后添加这些字符串的值(如果它们是相等的)

Question

如何比较保存在ArrayList中的对象中的字符串，然后添加这些字符串的值(如果它们是相等的)？

我知道如何检查StringX == StringY还是StringX.equals(StringY)，但无法理解如何比较ArrayList中的字符串，更不用说如何添加字符串对象中保持的双值(只有当该字符串相等时)。

示例类BaseBallTeam有两个属性；

• 字符串teamMember (例如Kat )
• 双homeRuns，例如2.0

我想把所有的homeRuns(双)加起来，由所有的Kats(string)组成。以及所有的homeRuns(双)由所有的麦克风等。

这是我的代码：

ArrayList<BaseBallTeam> list = new ArrayList<>();
double totalRuns = 0;
for(int i = 0; i<list.size();i++){
   for(int j = 1; j<list.size();j++){        
    if(list.get(i).getTeamMember().equals(list.get(j).getTeamMember())){
       totalRuns += list.get(j).getHomeRuns() +list.get(i).getHomeRuns();
       System.out.println("Amount of " + list.get(i).getTeamMember() + "s hit " + totalRuns"home runs);
   }
}                   

我的代码提供了所有团队成员累积的频率，而不是将两个单独的分数相加。

Answer 1

解决问题的最佳方法是使用java 8功能。您可以根据所有BaseBallTeam对象的名称和每个播放器的homeRuns总量与来自java.util.stream.Collectors的收集器对其进行分组：

样本代码：

    BaseBallTeam kate1 = new BaseBallTeam("Kate", 2);
    BaseBallTeam kate2 = new BaseBallTeam("Kate", 2);
    BaseBallTeam mike1 = new BaseBallTeam("Mike", 4);
    BaseBallTeam mike2 = new BaseBallTeam("Mike", 2);

    List<BaseBallTeam> list = Arrays.asList(kate1, kate2, mike1, mike2);
    Map<String, Integer> map = list.stream()
            .collect(Collectors.toMap(t -> t.getTeamMember(), 
                                      k -> k.getHomeRuns(), 
                                      (t1, t2) -> t1 + t2)
                    );
    System.out.println(map);

输出：{Mike=6，Kate=4}

在此：

1. Collectors.toMap说你想收集所有的团队到HashMap
2. T -> t.getTeamMember()表示按它们的teamMember(名称)收集。teamMember成为HashMap的关键
3. K -> k.getHomeRuns()表示将收集它们的homeRuns作为值
4. ( t1，t2) -> t1+ t2说，如果我们找到重复的键，我们想要和值

然后，您可以迭代您的地图如下：

map.entrySet().forEach(e -> 
               System.out.println("Amount of " + e.getKey() + "s hit " + e.getValue() + " home runs"));

产出：

迈克斯打了6次全垒打 凯特打了4次全垒打

Answer 2

你应该先看看团队成员是什么，然后你应该数他们的本垒打：

    ArrayList<BaseBallTeam> list = new ArrayList<>();
    // fill the list
    ArrayList<String> teamMembers = new ArrayList<>();
    for (int i = 0; i < list.size(); i++) {
        if (!teamMembers.contains(list.get(i).getTeamMember())) {
            teamMembers.add(list.get(i).getTeamMember());
        }
    }

    double totalRuns = 0;
    for (int i = 0; i < teamMembers.size(); i++) {
        double runs = 0;
        for (int j = 0; j < list.size(); j++) {
            if (list.get(j).getTeamMember().equals(teamMembers.get(i))) {
                runs += list.get(j).getHomeRuns();
            }
        }
        System.out.println("Amount of " + teamMembers.get(i) + "s hit " + runs + " home runs");
        totalRuns += runs;
    }
    System.out.println("Total homeruns " + totalRuns);

Answer 3

前面的答案效果很好。这里有一个简化代码和提高可读性的想法(不过，它也是这样做的！)：

BaseBallTeam kate1 = new BaseBallTeam("Kate", 2.0);
BaseBallTeam kate2 = new BaseBallTeam("Kate", 3.0);
BaseBallTeam mike1 = new BaseBallTeam("Mike", 1.0);
BaseBallTeam mike2 = new BaseBallTeam("Mike", 5.0);
List<BaseBallTeam> list = Arrays.asList(kate1, kate2, mike1, mike2);

ArrayList<String> teamMembers = new ArrayList<>();
for(BaseBallTeam team : list){
  if(!teamMembers.contains(team.getTeamMember())){
    teamMembers.add(team.getTeamMember());
  }
}

double totalRuns = 0;

for(String teamMember : teamMembers){
  double runs = 0;
  for(BaseBallTeam team : list){
    if(team.getTeamMember().equals(teamMember)){
      runs += team.getHomeRuns();
    }
  }
  System.out.println("Amount of " + teamMember + "s hit " + runs + " home runs");
  totalRuns += runs;
}
System.out.println("Total homeruns " + totalRuns);