package com.liupei.java8;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;


public class ListToMap {


    public static void main(String[] args) {
        List<Stu> stuList = new ArrayList<Stu>();
        //方式一
        Map<String, String> stringMap = stuList.stream().collect(Collectors.toMap(v -> String.valueOf(v.getId()), v -> v.getName()));
        //方式二
        Map<Long, String> stringMap2 = stuList.stream().collect(Collectors.toMap(Stu::getId, Stu::getName));

        //转换成map的时候，可能出现key一样的情况，如果不指定一个覆盖规则，上面的代码是会报错的。
        // 转成map的时候，最好使用下面的方式：
        Map<Long, Stu> maps = stuList.stream().collect(Collectors.toMap(Stu::getId, Function.identity(), (key1, key2) -> key2));

        Map<Long, String> maps1 = stuList.stream().collect(Collectors.toMap(Stu::getId, Stu::getName, (key1, key2) -> key2));

        //List 以ID分组 Map
        Map<Long, List<Stu>> groupBy = stuList.stream().collect(Collectors.groupingBy(Stu::getId));
    }
}

class Stu {
    private Long id;
    private String name;


    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}