[Java知识库]2021-10-28

```package com.springboot;

/**
 * @author chenLing
 * @version 0.0.1
 * @description TestVo
 * @since 2021/10/28 0028 21:49
 */
public class TestVO {
    private String name;
    private Integer old;
    private String work;

    @Override
    public String toString() {
        return "TestVO{" +
                "name='" + name + '\'' +
                ", old=" + old +
                ", work='" + work + '\'' +
                '}';
    }

    public TestVO(String name, Integer old, String work) {
        this.name = name;
        this.old = old;
        this.work = work;
    }

    public String getName() {
        return name;
    }

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

    public Integer getOld() {
        return old;
    }

    public void setOld(Integer old) {
        this.old = old;
    }

    public String getWork() {
        return work;
    }

    public void setWork(String work) {
        this.work = work;
    }
}

```java
package com.springboot;

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

/**
 * @author chenLing
 * @version 0.0.1
 * @description TestApp
 * @since 2021/10/28 0028 21:50
 */
public class TestApp {
    public static void main(String[] args) {
        List<TestVO> testVOList = new ArrayList<TestVO>();
        testVOList.add(new TestVO("小明",18,"student"))  ;
        testVOList.add( new TestVO("小明",20,"student"))  ;
        testVOList.add(new TestVO("小黄",20,"打铁的"))  ;
        testVOList.add(new TestVO("小黄",18,"打铁的"))  ;
        testVOList.add(new TestVO("小黑",18,"student"))  ;
        List<List<TestVO>> nameList = new ArrayList<>();
        testVOList.stream().collect(Collectors.groupingBy(TestVO::getName,
                Collectors.toList())).forEach((name,fooListByName)->{
            nameList.add(fooListByName);
                });
        for (List<TestVO> group: nameList) {
            System.out.println("nameList::"+group.size());
            System.out.println("nameList::"+group);
        }

        List<List<TestVO>> oldList = new ArrayList<>();
        testVOList.stream().collect(Collectors.groupingBy(TestVO::getName,
                Collectors.toList())).forEach((name,fooListByName)->{
            oldList.add(fooListByName);
                });

        for (List<TestVO> group: oldList) {
            System.out.println("oldList::"+group.size());
            System.out.println("oldList::"+group);
        }


        List<List<TestVO>> workList = new ArrayList<>();
        testVOList.stream().collect(Collectors.groupingBy(TestVO::getName,
                Collectors.toList())).forEach((name,fooListByName)->{
            workList.add(fooListByName);
                });

        for (List<TestVO> group: workList) {
            System.out.println("workList::"+group.size());
            System.out.println("workList::"+group);
        }


    }
}

输出如下：
nameList::2
nameList::[TestVO{name='小明', old=18, work='student'}, TestVO{name='小明', old=20, work='student'}]
nameList::1
nameList::[TestVO{name='小黑', old=18, work='student'}]
nameList::2
nameList::[TestVO{name='小黄', old=20, work='打铁的'}, TestVO{name='小黄', old=18, work='打铁的'}]
oldList::2
oldList::[TestVO{name='小明', old=18, work='student'}, TestVO{name='小明', old=20, work='student'}]
oldList::1
oldList::[TestVO{name='小黑', old=18, work='student'}]
oldList::2
oldList::[TestVO{name='小黄', old=20, work='打铁的'}, TestVO{name='小黄', old=18, work='打铁的'}]
workList::2
workList::[TestVO{name='小明', old=18, work='student'}, TestVO{name='小明', old=20, work='student'}]
workList::1
workList::[TestVO{name='小黑', old=18, work='student'}]
workList::2
workList::[TestVO{name='小黄', old=20, work='打铁的'}, TestVO{name='小黄', old=18, work='打铁的'}]