jdk1.8 lambda表达式处理集合的一些用法

package com.kerry;

import java.time.Clock;
import java.time.Duration;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.Month;
import java.util.Arrays;
import java.util.Calendar;
import java.util.Collection;
import java.util.Collections;
import java.util.Date;
import java.util.List;
import java.util.Map;
import java.util.OptionalInt;
import java.util.TimeZone;
import java.util.stream.Collectors;

public class JDK8Test {

public static void streamTest(){

List<Task> tasks =Arrays.asList(new Task("OPEN", 3),new Task("PENDING", 6),
new Task("PENDING", 6),new Task("CLOSE", 10),new Task("OPEN", 5));

//循环
tasks.forEach(task -> {
//处理逻辑.....
if (task.getStatus().equals("OPEN")) {
// .task....
}
});

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

//过滤list
List<Task> filterTasks = tasks.stream()
.filter(t -> t.getStatus() == "OPEN" && t.getScore()==3)
.collect(Collectors.toList());

//获取集合最大最小值
OptionalInt max = tasks.stream()
.filter( task -> task.getStatus() == "OPEN" )//过滤条件
.mapToInt(Task::getScore)
.max();//获取open状态最大的值
// .min();//获取open状态最小的值

//求和
int totalOpenScore = tasks.stream()
.filter( task -> task.getStatus() == "OPEN" )//过滤条件
.mapToInt(task -> task.getScore()) // Task::getScore
.sum(); //获取open状态的值求和

//并行计算求和
int totalScore = tasks.stream()
.parallel()
.map(task -> task.getScore())
.reduce(0, Integer::sum);

//分组统计
Map<String, List<Task>> map = tasks.stream().
collect(Collectors.groupingBy(Task::getStatus));

//求百分比
Collection<String > result =
tasks.stream()
.mapToInt(Task::getScore)
.asLongStream()
.mapToDouble(score -> (float)score / totalScore)
.boxed()
.mapToLong(weight -> (long)(weight*100))
.mapToObj(percent ->percent+"%")
.collect(Collectors.toList());

System.out.println("各百分比："+result);
System.out.println("分组统计:"+map);
System.out.println("过滤求和："+totalOpenScore);
System.out.println("最大值："+max.getAsInt());
System.out.println("总计："+totalScore);
}

public static void main(String args[]) {
streamTest();

Clock c = Clock.systemDefaultZone();
System.out.println(c.instant());
System.out.println(c.millis());
LocalDateTime ldt = LocalDateTime.now();
System.out.println(ldt);
System.out.println(LocalTime.now());
System.out.println(LocalDate.now());

// Get duration between two dates
final LocalDateTime from = LocalDateTime.of( 2014, Month.APRIL, 16, 0, 0, 0 );
final LocalDateTime to = LocalDateTime.of( 2015, Month.APRIL, 16, 0, 0, 0 );

final Duration duration = Duration.between( from, to );
System.out.println( "Duration in days: " + duration.toDays() );
System.out.println( "Duration in hours: " + duration.toHours() );

}
}


package com.kerry;

public class Task {

private String status;
private Integer score;

public Task(String status, Integer score) {
this.status = status;
this.score = score;
}
public String getStatus() {
return status;
}
public void setStatus(String status) {
this.status = status;
}
public Integer getScore() {
return score;
}
public void setScore(Integer score) {
this.score = score;
}
@Override
public String toString() {
return "Task [status=" + status + ", score=" + score + "]";
}

}