今天給大家說說怎麼把TreeMap 的值進行排序,TreeMap 預設排序規則：按照key的字典順序來排序（升序）
而HashMap在放入的時候已經內部規定好排序了,TreeMap可以可以自定義排序,廢話不多說,上程式碼!
    首先,這裡建立了一個User類如下:

public class User {
    private String name;
    private int age;
    private int id;

    @Override
    public String toString() {
        return "User [name="
 
 + name + ", age=" + age + ", id=" + id + "]";
    }

    public User(String name, int age, int id) {
        super();
        this.name = name;
        this.age = age;
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public int getId() {
        return id;
    }

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

    然後呢,根據鍵排序,建立測試類如下:

import java.util.ArrayList;
 

import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.TreeMap;

public class Test {
    public static void main(String[] args) {
        Map<Integer, User> map = new TreeMap<>(new Comparator<Integer>() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return o1 - o2;
            }
        });
        map.put(5, new User("張三", 12, 3));
        map.put(6, new User("李四", 14, 4));
        map.put(2, new User("王五", 10, 9));
        map.put(9, new User("趙六", 19, 1));
        map.put(3, new User("宋琦", 22, 7));
        map.put(6, new User("關羽", 8, 6));
        // 根據鍵來排序
        Iterator<Entry<Integer, User>> iter = map.entrySet().iterator();
        while (iter.hasNext()) {
            System.out.print(iter.next().getKey() + "\t");
        }

    下來就是根據值排序了,我們先根據年齡排序:

        List<Map.Entry<Integer, User>> list = new ArrayList<>(map.entrySet());
        Collections.sort(list, new Comparator<Map.Entry<Integer, User>>() {
            @Override
            public int compare(Entry<Integer, User> o1, Entry<Integer, User> o2) {
                return o1.getValue().getAge() - o2.getValue().getAge();
            }
        });

        for (Entry<Integer, User> entry : list) {
            System.out.print(entry.getValue().getAge() + "\t");
        }

    再下來我們根據id排序:

        List<Map.Entry<Integer, User>> list2 = new ArrayList<Map.Entry<Integer, User>>(map.entrySet());
        Collections.sort(list2, new Comparator<Map.Entry<Integer, User>>() {
            @Override
            public int compare(Entry<Integer, User> o1, Entry<Integer, User> o2) {
                return o1.getValue().getId() - o2.getValue().getId();
            }
        });
        for (Entry<Integer, User> entry : list2) {
            System.out.print(entry.getValue().getId() + "\t");
        }

    **我們在排序值得時候,是把TreeMap放到List裡進行排序,所以,取出來的時候也是必須要從list裡取**
      好了.今天的分享就到這裡,如果發現錯誤請及時聯絡更改,以免誤人子弟!