Java8新特性之Steam
2022/8/6 1:23:52
本文主要是介绍Java8新特性之Steam,对大家解决编程问题具有一定的参考价值,需要的程序猿们随着小编来一起学习吧!
package com.demo; import org.testng.annotations.Test; import java.util.ArrayList; import java.util.List; import java.util.Optional; import java.util.stream.Collectors; import java.util.stream.Stream; public class StreamTest { @Test public void test1() { //实例化Steam List<People> list = People.getPeopleList(); Stream<People> stream = list.stream(); // 1. 筛选与切片 System.out.println("只打印第一个============="); stream.limit(1).forEach(System.out::println); // 流被终止后只能重新实例化 System.out.println("跳过前两个============"); list.stream().skip(2).forEach(System.out::println); System.out.println("筛选出性别为女的============"); list.stream().filter(e -> e.getSex().equals("女")).forEach(System.out::println); // 2. 映射,可以理解为会对集合里每个元素都进行的一个操作 System.out.println("打印出每个对象的名字============"); list.stream().map(People::getName).forEach(System.out::println); System.out.println("在每个对象名字后面加上一个+号并打印出来============"); list.stream().map(People::getName).map(e -> e += "+").forEach(System.out::println); //3. 排序 // System.out.println("排序会报错,因为People没有实现comparable接口============"); // list.stream().sorted().forEach(System.out::println); System.out.println("根据年龄排序============"); list.stream().sorted( (o1, o2) -> { if (o1.getAge() == o2.getAge()) { return o1.getName().compareTo(o2.getName()); } return Integer.compare(o1.getAge(), o2.getAge()); } ).forEach(System.out::println); //4. 匹配与查找 System.out.println("是否所有的对象都是男性============"); System.out.println(list.stream().allMatch(e -> e.getSex().equals("男"))); System.out.println("是否有一个对象是男性============"); System.out.println(list.stream().anyMatch(e -> e.getSex().equals("男"))); System.out.println("是否没有一个对象是男性============"); System.out.println(list.stream().noneMatch(e -> e.getSex().equals("男"))); System.out.println("打印出第一个对象============"); System.out.println(list.stream().findFirst()); //5.规约 System.out.println("求所有对象年龄的综合============"); Optional<Integer> reduce = list.stream().map(People::getAge).reduce(Integer::sum); System.out.println(reduce); System.out.println("把所有性别为男的对象的年龄放到一个新的列表里面============"); List<Integer> collect = list.stream().filter(e -> e.getSex().equals("男")).map(People::getAge).collect(Collectors.toList()); System.out.println(collect); } } class People { String name; String sex; int age; public People(String name, String sex, int age) { this.name = name; this.sex = sex; this.age = age; } public static List<People> getPeopleList() { List<People> peopleList = new ArrayList<>(); People people = new People("雷军", "男", 45); People people1 = new People("马云", "男", 45); People people2 = new People("任正非", "男", 77); People people3 = new People("董明珠", "女", 44); peopleList.add(people); peopleList.add(people1); peopleList.add(people2); peopleList.add(people3); return peopleList; } @Override public String toString() { return "People{" + "name='" + name + '\'' + ", sex='" + sex + '\'' + ", age=" + age + '}'; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } }
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