java - 与 Java Streams 并行循环？

Question

我有两个列表。其中显示了一组人中每个人对某个游戏的成功尝试次数。

public class SuccessfulAttempts{
    String name;
    int successCount;
}

List<SuccessfulAttempts> success;

以及每个人的总尝试次数。

public class TotalAttempts{
    String name;
    int totalCount;
}

List<TotalAttempts> total;

我想显示小组中每个人的成功百分比。

public class PercentageSuccess{
    String name;
    float percentage;
}

List<PercentageSuccess> percentage;

假设我已经像这样填充了前两个列表。

success.add(new SuccessfulAttempts(Alice, 4));
success.add(new SuccessfulAttempts(Bob, 7));

total.add(new TotalAttempts(Alice, 5));
total.add(new TotalAttempts(Bob, 10));

现在我想计算每个人使用 Java Streams 的成功百分比。所以我实际上需要列表的这种结果 List<PercentageSuccess> percentage .

new PercentageSuccess(Alice, 80);
new PercentageSuccess(Bob, 70);

我想并行计算它们(爱丽丝的百分比和鲍勃的百分比)(我知道如何使用循环按顺序进行)。我如何使用 Java Streams(或任何其他简单的方法)实现这一点？？

Answer 1

我建议将您的其中一个列表转换为 map ，以便更轻松地访问计数。否则，对于一个列表的每个值，您必须在另一个列表中循环，这将是 O(n^2) 复杂性。

List<SuccessfulAttempts> success = new ArrayList<>();
List<TotalAttempts> total = new ArrayList<>();

success.add(new SuccessfulAttempts("Alice", 4));
success.add(new SuccessfulAttempts("Bob", 7));

total.add(new TotalAttempts("Alice", 5));
total.add(new TotalAttempts("Bob", 10));

// First create a Map
Map<String, Integer> attemptsMap = success.parallelStream()
    .collect(Collectors.toMap(SuccessfulAttempts::getName, SuccessfulAttempts::getSuccessCount));

// Loop through the list of players and calculate percentage.
List<PercentageSuccess> percentage =
    total.parallelStream()
         // Remove players who have not participated from List 'total'. ('attempt' refers to single element in List 'total').
         .filter(attempt -> attemptsMap.containsKey(attempt.getName()))
         // Calculate percentage and create the required object
         .map(attempt -> new PercentageSuccess(attempt.getName(),
                    ((attemptsMap.get(attempt.getName()) * 100) / attempt.getTotalCount())))
         // Collect it back to list
         .collect(Collectors.toList());

percentage.forEach(System.out::println);