Java进阶学习笔记56——Stream

Stream流的初体验：

package cn.chang.d8_stream;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.stream.Collectors;

public class StreamTest1 {
    public static void main(String[] args) {
        List<String> names = new ArrayList<String>();
        Collections.addAll(names, "张三丰", "张无忌", "周芷若", "赵敏", "张强");
        System.out.println(names);

        // 找出姓张，且是3个字的名字，存入到一个新的集合中去
//        List<String> list = new ArrayList<>();
//        for (String name : names) {
//            if(name.startsWith("张") && name.length() == 3) {
//                list.add(name);
//            }
//        }
//        System.out.println(list);

        // 开始使用Stream流来解决这个需求：
        List<String> list2 = names.stream().filter(s -> s.startsWith("张")).filter(a -> a.length() == 3).collect(Collectors.toList());
        System.out.println(list2);
    }
}

运行结果：

Stream流的使用步骤：

Stream流的常用方法：

 获取Stream流：

获取集合的Stream流：

代码：

package cn.chang.d8_stream;

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

public class StreamTest2 {
    public static void main(String[] args) {
        // 1. 如何获取List集合的Stream流？
        List<String> names = new ArrayList<String>();
        Collections.addAll(names, "张三丰", "张无忌", "周芷若", "赵敏", "张强");

        Stream<String> stream = names.stream();

        // 2. 如何获取Set集合的Stream流？
        Set<String> set = new HashSet<String>();
        Collections.addAll(set, "刘德华", "张曼玉", "蜘蛛精", "马德", "德玛西亚");

        Stream<String> stream2 = set.stream();
        stream2.filter(s -> s.contains("德")).forEach(s -> System.out.println(s));

        // 3. 如何获取Map集合的Stream流？
        Map<String, Double> map = new HashMap<>();
        map.put("古力娜扎", 172.3);
        map.put("迪丽热巴", 168.3);
        map.put("马尔扎哈", 166.3);
        map.put("卡尔扎巴", 168.3);

//        map.Stream();
        Set<String> keys = map.keySet();
        Stream<String> ks = keys.stream();

        Collection<Double> values = map.values();
        Stream<Double> vs = values.stream();

        Set<Map.Entry<String, Double>> entries = map.entrySet();
        Stream<Map.Entry<String, Double>> kvs = entries.stream();

        kvs.filter(e -> e.getKey().contains("巴")).forEach(e -> System.out.println(e.getKey() + "-->" + e.getValue()));

        // 4. 如何获取数组的Stream流？
        String[] names2 = {"张翠山", "东方不败", "唐大山", "独孤求败"};
        Stream<String> s1 = Arrays.stream(names2);
        Stream<String> s2 = Stream.of(names2);

        
    }
}