JDK1.8新特性：＜一＞Stream流基操

import org.junit.Test;

import java.text.Collator;
import java.util.*;
import java.util.stream.Collectors;

public class Stream {

    /**
     * 中间操作
     */
    @Test
    public void filter(){
        List list = Arrays.asList("米哈游a","阿里a","未知c","华为d","天美a","京东d","饿了么s","网易s","腾讯a","百度a");
        //1,创建流 ①创建普通流stream(); ②创建并行流 parallelStream();
        //2,中间操作: filter()设置过滤条件 str是集合里的每一个元素
        //3,最终操作:collect()
        // 将含有字母a的元素返回组成一个新的集合result
        List result = list.stream().filter(str -> str.contains("a")).collect(Collectors.toList());
        System.out.println(result); // [米哈游a, 阿里a, 天美a, 腾讯a, 百度a]
    }

    @Test
    public void distinct1(){
        List list = Arrays.asList("米哈游a","米哈游a","米哈游a","阿里a","未知c","未知c","华为d","天美a","京东d","饿了么s","网易s","腾讯a","百度a");
        //distinct()去重
        List result = list.stream().distinct().collect(Collectors.toList());
        System.out.println(result); //[米哈游a, 阿里a, 未知c, 华为d, 天美a, 京东d, 饿了么s, 网易s, 腾讯a, 百度a]
    }

    @Test
    public void distinct2(){
        //如果集合是对象,distinct()操作的地址引用,只要地址不同那么对象都是不同的
        List users = new ArrayList<>();
        users.add(new User("a","33"));
        users.add(new User("a","33"));
        users.add(new User("a","33"));
        users.add(new User("a","33"));
        List resUser = users.stream().distinct().collect(Collectors.toList());
        //[User{name='a', age='33'}, User{name='a', age='33'}, User{name='a', age='33'}, User{name='a', age='33'}]
        System.out.println(resUser);
    }

    @Test
    public void limit(){
        //limit()从集合的前面开始拿n个元素
        List prices = Arrays.asList("13RMB","free","37RMB","free","8RMB","free","8RMB","20RMB","free","2RMB");
        List collect = prices.stream().limit(4).collect(Collectors.toList());
        System.out.println(collect); //[13RMB, free, 37RMB, free]
    }

    @Test
    public void skip(){
        //skip()返回扔掉前n个元素后的集合
        List prices = Arrays.asList("13RMB","free","37RMB","free","8RMB","free","8RMB","20RMB","free","2RMB");
        List collect = prices.stream().skip(5).collect(Collectors.toList());
        System.out.println(collect); //[free, 8RMB, 20RMB, free, 2RMB]
    }

    @Test
    public void map(){
        //map() 对流中所有数据做统一处理
        List prices = Arrays.asList("13RMB","free","37RMB","free","8RMB","free","8RMB","20RMB","free","2RMB");
        List result = prices.stream().map(str ->"￥"+str).collect(Collectors.toList());
        //[￥13RMB, ￥free, ￥37RMB, ￥free, ￥8RMB, ￥free, ￥8RMB, ￥20RMB, ￥free, ￥2RMB]
        System.out.println(result);
    }

    @Test
    public void flatMap(){
        //flatMap()扁平化操作
    }

    @Test
    public void sorted(){
        //sorted()将流排序后输出 默认从升序

//        数字排序
        List ins = Arrays.asList(234,34,25,45,26,-235,-56,232,67,2,45,134,0,453,23);
        List collect = ins.stream().sorted().collect(Collectors.toList());
        //[-235, -56, 0, 2, 23, 25, 26, 34, 45, 45, 67, 134, 232, 234, 453]
        System.out.println(collect);

//        字母排序
        List strs = Arrays.asList("as","ad","gea","jws","afr","cvw","te","yue");
        List collect1 = strs.stream().sorted().collect(Collectors.toList());
        // [ad, afr, as, cvw, gea, jws, te, yue]
        System.out.println(collect1);

        //汉字排序 传入一个比较器
        List characters = Arrays.asList("张","杨","找","哈","啊","你","哦","都","回");
        List collect2 = characters.stream().sorted(Collator.getInstance(Locale.CHINA)).collect(Collectors.toList());
        // [啊, 都, 哈, 回, 你, 哦, 杨, 张, 找]
        System.out.println(collect2);
    }



    /**
     * 终止操作
     */
    @Test
    public void anyMatch(){
        //anyMatch()集合中是否有至少一个元素满足条件 返回boolean
        List prices = Arrays.asList("13RMB","free","37RMB","free","8RMB","free","8RMB","20RMB","free","2RMB");
        boolean isFree = prices.stream().anyMatch(str -> str.contains("free"));
        System.out.println(isFree); //true
    }

    @Test
    public void allMatch(){
        //allMatch()元素是否都满足条件
        List prices = Arrays.asList("13RMB","free","37RMB","free","8RMB","free","8RMB","20RMB","free","2RMB");
        boolean b = prices.stream().allMatch(str -> str.length() > 3);
        System.out.println(b); //true
    }

    @Test
    public void noneMatch(){
        //noneMatch() 集合所有的元素都不满足条件
        List prices = Arrays.asList("13RMB","free","37RMB","free","8RMB","free","8RMB","20RMB","free","2RMB");
        boolean b = prices.stream().noneMatch(str -> str.length() > 13);
        System.out.println(b); //true
    }

    @Test
    public void findAny(){
        //findAny()返回集合中的任意元素 如何使用的是stream()串行流则总是拿到第一个,并行流则会是随机的
        List prices = Arrays.asList("13RMB","free","37RMB","free","8RMB","free","8RMB","20RMB","free","2RMB");
        Optional any = prices.stream().findAny();
        if (any.isPresent()){
            System.out.println(any.get()); //13RMB
        }

        Optional any1 = prices.parallelStream().findAny();
        System.out.println(any1.get()); //8RMB
    }

    @Test
    public void findFirst(){
        List prices = Arrays.asList("13RMB","free","37RMB","free","8RMB","free","8RMB","20RMB","free","2RMB");
        Optional any = prices.stream().findFirst();
        System.out.println(any); //Optional[13RMB]
    }

    @Test
    public void forEach(){
        //forEach()遍历集合
        List list = Arrays.asList("2022-6-1","2022-3-20","2022-7-12","2022-4-26","2022-5-9","2022-5-28","2022-10-3");
        //传统
        list.forEach(System.out::println);
        //流
        list.stream().forEach(System.out::println);
    }

    @Test
    public void collect(){
        //collect()收集器
        List list = Arrays.asList("2022-6-1","2022-3-20","2022-3-20","2022-4-26","2022-4-26","2022-5-28","2022-10-3");

        //收集为Set集合
        Set collect = list.stream().collect(Collectors.toSet());
        //[2022-6-1, 2022-10-3, 2022-3-20, 2022-4-26, 2022-5-28]
        System.out.println(collect);

        //收集为Map集合
        //参数说明: k-> k使用key v->v 使用的value  (oldV, newV) -> newV当值重复的时候用新值贴换
        Map collect1 = list.stream().collect(Collectors.toMap(k -> k, v -> v, (oldV, newV) -> newV));
        //{2022-10-3=2022-10-3,
        // 2022-6-1=2022-6-1,
        // 2022-3-20=2022-3-20,
        // 2022-4-26=2022-4-26,
        // 2022-5-28=2022-5-28}
        System.out.println(collect1);

    }

    @Test
    public void reduce(){
        //reduce()可以将元素中的值反复结合起来得到一个结果
        List characters = Arrays.asList("张","杨","找","哈","啊","你","哦","都","回");
        /*
            (accumulator, item) -> { //第一个参数是计算结果,第二个参数是集合中的每个元素
                return accumulator+item;
            }
         */
        Optional reduce = characters.stream().reduce((accumulator, item) -> {
            return accumulator+item;
        });
        System.out.println(reduce.get()); //张杨找哈啊你哦都回
    }

    @Test
    public void count(){
        //count()获取元素中的个数
        List characters = Arrays.asList("张","杨","找","哈","啊","你","哦","都","回");
        long count = characters.stream().count();
        System.out.println(count); //9
    }
}

写在后面的话

        emm，因为最近半年一直在忙于学习各种技术，没时间写博客，最近在自己准备写一个权限框架，想着复习一下基础，故此今日写了点小demo，希望大家以后学以致用！！