Stream流操作

蔚落 2022-06-08 00:56 285阅读 0赞

#### stream流操作 ####

public class Streams { 
    
        private enum Status{
            OPEN,CLOSE
        };
    
        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 );
            }
        }
    
        /** * Stream操作测试：stream操作分为：中间操作，例如filter()仍然返回一个Stream； * 晚期操作，例如sum()、forEach()，这些操作会遍历stream获取结果，在执行晚期操作以后 * stream处理线程处理完毕 * @see Collection#stream() * @see java.util.stream.Stream#filter(Predicate) * @desc 这里Task::getPoints方法引用和task->task.getPoints效果相同 */
        @Test
        public void streamTest(){
            final Collection<Task> tasks = Arrays.asList(
                    new Task(Status.OPEN,5),
                    new Task(Status.OPEN,13),
                    new Task(Status.CLOSE,8)
            );
            final long totalPoints = tasks.stream()
                    .filter(task -> task.getStatus().equals(Status.OPEN))
                    .mapToInt(Task::getPoints)
                    .sum();
            System.out.println("totalPoints:" + totalPoints);
        }
    }

#### 并行处理 ####

/** * java8另一特性：创造性支持了并行处理（parallel processing） * 这里使用parallel方法并行处理所有task，并用reduce方法计算出最终结果 * * @see Stream#parallel() * @see Stream#reduce(Object, BinaryOperator) */
    @Test
    public void parallelProcessTest(){
        final Collection<Task> tasks = Arrays.asList(
                new Task(Status.OPEN,5),
                new Task(Status.OPEN,13),
                new Task(Status.CLOSE,8)
        );
        final long totalPoints = tasks.stream()
                .parallel()
                .map(task -> task.getPoints())
                .reduce(0,Integer::sum);
        System.out.println("totalPoints:" + totalPoints);
    }