package staticTest;

import java.util.Arrays;
import java.util.Collection;

public class Streams {
private enum Status {
OPEN, CLOSED
};

private static final class Task {
private final Status status;
private final Integer points;

  Task(final Status status, final Integer points) {
   this.status = status;
   this.points = points;
  }

  public Integer getPoints() {
   return points;
  }

  public Status getStatus() {
   return status;
  }

  @Override
  public String toString() {
   return String.format("[%s, %d]", status, points);
  }
}

public static void main(String args[]) {
  final Collection<Task> tasks = Arrays.asList(
    new Task(Status.OPEN, 5),
    new Task(Status.OPEN, 13),
    new Task(Status.CLOSED, 8)
    );

  // Calculate total points of all active tasks using sum()
  final long totalPointsOfOpenTasks = tasks.stream().filter(task -> task.getStatus() == Status.OPEN)
    .mapToInt(Task::getPoints).sum();

System.out.println("Total points: " + totalPointsOfOpenTasks);
}

}

处理过程

task集合被转化为stream流对像，通过filter过滤数据，只取status为OPEN的。

mapToInt操作通过Task::getPoints这种方式调用每个task实例的getPoints方法把Task的stream转化为Integer的stream。

最后，用sum函数把所有的分数加起来，得到最终的结果。

ITPub博客

java 8 Stream处理

最新文章