stream学习（一）

package com.test;

import com.test.dao.Person;

import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class TestApplication {
    static List<Person> personList = new ArrayList<Person>();
    private static void initPerson() {
        personList.add(new Person("张三", 8, 3000));
        personList.add(new Person("李四", 18, 5000));
        personList.add(new Person("王五", 28, 7000));
        personList.add(new Person("孙六", 38, 9000));
    }
    public static void main(String[] args) {
        List<Integer> list = Arrays.asList(7, 6, 9, 3, 8, 2, 1);

        // 遍历输出符合条件的元素
        list.stream().filter(x -> x > 6).forEach(System.out::println);
        // 匹配第一个
        Optional<Integer> findFirst = list.stream().filter(x -> x > 6).findFirst();
        // 匹配任意（适用于并行流）
        Optional<Integer> findAny = list.parallelStream().filter(x -> x > 6).findAny();
        // 是否包含符合特定条件的元素
        boolean anyMatch = list.stream().anyMatch(x -> x < 6);
        System.out.println("匹配第一个值：" + findFirst.get());
        System.out.println("匹配任意一个值：" + findAny.get());
        System.out.println("是否存在大于6的值：" + anyMatch);
        filter01();
        test02();
        test05();
        test06();
        test07();
        test08();
        test09();
        test10();
        test11();
        test13();
        test14();
//        test15();  有报错
        test16();
    }

    /**
     * 筛选员工中未满18周岁的人，并形成新的集合
     * @思路
     * List<Person> list = new ArrayList<Person>();
     * for(Person person : personList) {
     *     if(person.getAge() > 18) {
     *          list.add(person);
     *     }
     * }
     */
    private static void filter01(){
        initPerson();
        //（1）筛选员工中未满18周岁的人，并形成新的集合
        List<Person> collect = personList.stream().filter(x -> x.getAge()> 18).collect(Collectors.toList());
        System.out.println("filter01:"+collect);

    }

    /**
     * 获取String集合中最长的元素
     * @思路
     * List<String> list = Arrays.asList("zhangsan", "lisi", "wangwu", "sunliu");
     * String max = "";
     * int length = 0;
     * int tempLength = 0;
     * for(String str : list) {
     *     tempLength = str.length();
     *     if(tempLength > length) {
     *         length  = str.length();
     *         max = str;
     *      }
     * }
     * @return zhangsan
     */
    private static void test02(){
        List<String> list = Arrays.asList("zhangsan", "lisi", "wangwu", "sunliu");
        //比较传入条件是比较字符串的长度
        Comparator<? super String> comparator = Comparator.comparing(String::length);
        Optional<String> max = list.stream().min(comparator);
        System.out.println(max);
    }
    //（2）获取Integer集合中的最大值
    private static void test05() {
        List<Integer> list = Arrays.asList(1,4,7,34,23,67,54);
        Optional<Integer> max = list.stream().max(Integer::compareTo);
        //自定义排序
        Optional<Integer> max1 = list.stream().min(new Comparator<Integer>() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return o1.compareTo(o2);
            }
        });
        System.out.println(max1);

    }
    //获取员工中年龄最大的人
    private static void test06() {
        initPerson();
        Comparator<Person> anInt = Comparator.comparingInt(Person::getAge);
        Optional<Person> max = personList.stream().max(anInt);
        System.out.println(max);

    }
    //（4）计算integer集合中大于10的元素的个数
    private static void test07() {
        List<Integer> list = Arrays.asList(1, 23, 32, 2, 54, 14);
        long count = list.stream().filter(x -> x > 10).count();
        Optional<Integer> max = list.stream().filter(x -> x > 10).max(Integer::compareTo);
        System.out.println("count:"+count+"max:"+max);
    }
    //map和flatMap
    private static void test08() {
        List<String> list = Arrays.asList("zhangsan", "lisi", "wangwu", "sunliu");
//        list.stream().forEach(x -> x.toUpperCase());
        //（1）字符串大写
        List<String> collect = list.stream().map(x -> x.toUpperCase()).collect(Collectors.toList());
        List<String> collect1 = list.stream().map(String::toUpperCase).collect(Collectors.toList());
        System.out.println(collect);
        System.out.println(collect1);
    }
    //（2）整数数组每个元素+3
    /**
     * 整数数组每个元素+3
     * @思路
     * List<Integer> list = Arrays.asList(1, 17, 27, 7);
    List<Integer> list2 = new ArrayList<Integer>();
    for(Integer num : list) {
    list2.add(num + 3);
    }
     @return [4, 20, 30, 10]
     */
    private static void test09() {
        List<Integer> list = Arrays.asList(1, 17, 27, 7);
        List<Integer> collect = list.stream().map(x -> x + 3).collect(Collectors.toList());
        System.out.println(collect);
    }
    //公司效益好每人涨两千
    private static void test10() {
        initPerson();
        List<Object> collect = personList.stream().map(x -> {
            x.setSalary(x.getSalary() + 2000);
            return x;
        }).collect(Collectors.toList());
        System.out.println(collect);
    }

    //（4）将两个字符数组合并成一个新的字符数组
    private static void test11() {
        String[] arr = {"z, h, a, n, g", "s, a, n"};
        List<String> list = Arrays.asList(arr);
        System.out.println(list);
        List<String> collect = list.stream().flatMap(x -> {
            String[] array = x.split(",");
            Stream<String> stream = Arrays.stream(array);
            return stream;
        }).collect(Collectors.toList());
        System.out.println(collect);
    }


    //（1）求Integer集合的元素之和、乘积和最大值
    private static void test13() {
        List<Integer> list = Arrays.asList(1, 2, 3, 4);
        Optional<Integer> reduce = list.stream().reduce((x, y) -> x + y);
        System.out.println("求和:"+reduce);
        //求积
        Optional<Integer> reduce2 = list.stream().reduce((x,y) -> x * y);
        System.out.println("求积:"+reduce2);
        //求最大值
        Optional<Integer> reduce3 = list.stream().reduce((x,y) -> x>y?x:y);
        System.out.println("求最大值:"+reduce3);
    }

    //（2）求所有员工的工资之和和最高工资
    private static void test14() {
        initPerson();
        Optional<Integer> reduce = personList.stream().map(Person::getSalary).reduce(Integer::sum);
        Optional<Integer> reduce2 = personList.stream().map(Person :: getSalary).reduce(Integer::max);
        System.out.println("工资之和:"+reduce);
        System.out.println("最高工资:"+reduce2);
    }

    //6、收集（toList、toSet、toMap）
    //取出大于18岁的员工转为map
    private static void test15(){
        initPerson();
        Map<String, Person> collect1 = personList.stream().filter(x -> x.getAge() > 18).collect(Collectors.toMap(Person::getName, y -> y));
        System.out.println(collect1);

    }

    /*7、collect
    Collectors提供了一系列用于数据统计的静态方法：
    计数： count
    平均值： averagingInt、 averagingLong、 averagingDouble
    最值： maxBy、 minBy
    求和： summingInt、 summingLong、 summingDouble
    统计以上所有： summarizingInt、 summarizingLong、 summarizingDouble
     */
    private static void test16(){
        initPerson();
        //统计员工人数
        Long collect = personList.stream().collect(Collectors.counting());
        System.out.println("统计员工人数:"+collect);
        //求平均工资
        Double collect1 = personList.stream().collect(Collectors.averagingDouble(Person::getSalary));
        System.out.println("求平均工资:"+collect);
        //求最高工资
        Optional<Integer> collect2 = personList.stream().map(Person::getSalary).collect(Collectors.maxBy(Integer::compareTo));
        System.out.println("求最高工资:"+collect2);
        //求工资之和
        Integer collect3 = personList.stream().collect(Collectors.summingInt(Person::getSalary));
        System.out.println("求最高工资:"+collect3);
        //一次性统计所有信息
        DoubleSummaryStatistics collect4 = personList.stream().collect(Collectors.summarizingDouble(Person::getSalary));
        System.out.println("一次性统计所有信息:"+collect4);
    }
    /**
     * 8、分组(partitioningBy/groupingBy)
     * 分区：将stream按条件分为两个 Map，比如员工按薪资是否高于8000分为两部分。
     *
     * 分组：将集合分为多个Map，比如员工按性别分组。有单级分组和多级分组。
     */


}