Java语言利用Collections.sort对Map,List排序

Posted 2020-11-09 缘故为何

1.main方法包含TreeMap排序1，TreeMap排序2，HashMap排序，List<Integer>排序，List<Bean>排序，List<Map>排序

package com.tao.test;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.TreeMap;

public class Sort {
    public static void main(String[] args) {
        // TreeMap排序1
        Map<String, String> treeMap = new TreeMap<String, String>(new Comparator<String>() {
            public int compare(String o1, String o2) {
                // 升序排序
                return o1.compareTo(o2);
            }
        });
        treeMap.put("c", "ccccc");
        treeMap.put("a", "aaaaa");
        treeMap.put("b", "bbbbb");
        treeMap.put("d", "ddddd");
        // 排序后输出
        for (String key : treeMap.keySet()) {
            System.out.println("Key=" + key + ", Value=" + treeMap.get(key));
        }

        // TreeMap排序2
        Map<String, Integer> treeMap2 = new TreeMap<String, Integer>();
        treeMap2.put("d", 3);
        treeMap2.put("b", 4);
        treeMap2.put("a", 7);
        treeMap2.put("c", 1);
        // 转换成list
        List<Map.Entry<String, Integer>> treeList = new ArrayList<Map.Entry<String, Integer>>(treeMap2.entrySet());
        Collections.sort(treeList, new Comparator<Map.Entry<String, Integer>>() {
            // 升序排序
            public int compare(Entry<String, Integer> o1, Entry<String, Integer> o2) {
                return o1.getValue().compareTo(o2.getValue());
            }
        });
        // 排序后输出
        for (Map.Entry<String, Integer> m : treeList) {
            System.out.println("Key=" + m.getKey() + ", Value=" + m.getValue());
        }

        // HashMap排序
        Map<String, Integer> hashMap = new HashMap<String, Integer>();
        hashMap.put("c", 3);
        hashMap.put("a", 2);
        hashMap.put("b", 1);
        hashMap.put("d", 4);
        List<Map.Entry<String, Integer>> hashList = new ArrayList<Map.Entry<String, Integer>>(hashMap.entrySet());
        Collections.sort(hashList, new Comparator<Map.Entry<String, Integer>>() {
            // 升序排序
            public int compare(Entry<String, Integer> o1, Entry<String, Integer> o2) {
                return o1.getValue().compareTo(o2.getValue());
            }
        });
        // 排序后输出
        for (Map.Entry<String, Integer> m : hashList) {
            System.out.println("Key=" + m.getKey() + ", Value=" + m.getValue());
        }

        // List<Integer>排序
        List<Integer> nums = new ArrayList<Integer>();
        nums.add(3);
        nums.add(5);
        nums.add(2);
        nums.add(1);
        // 升序排序（默认）
        Collections.sort(nums);
        // 排序后输出
        System.out.println(nums);

        // List<Bean>排序
        List<User> users = new ArrayList<User>();
        users.add(new User(2, "jack"));
        users.add(new User(1, "tom"));
        users.add(new User(3, "keck"));
        users.add(new User(4, "tao"));
        // id升序排序
        Collections.sort(users);
        // 排序后输出
        for (User user : users) {
            System.out.println(user.getId() + "," + user.getName());
        }

        // List<Map>排序
        List<Map<String, Integer>> listMap = new ArrayList<Map<String, Integer>>();
        Map<String, Integer> map = new HashMap<>();
        map.put("age", 20);
        map.put("sex", 1);
        listMap.add(map);
        Map<String, Integer> map2 = new HashMap<>();
        map2.put("age", 29);
        map2.put("sex", 2);
        listMap.add(map2);
        Map<String, Integer> map3 = new HashMap<>();
        map3.put("age", 35);
        map3.put("sex", 1);
        listMap.add(map3);
        // 按照map值排序
        Collections.sort(listMap, new Comparator<Map<String, Integer>>() {
            @Override
            public int compare(Map<String, Integer> o1, Map<String, Integer> o2) {
                return o1.get("age").compareTo(o2.get("age"));// age升序排序
            }
        });
        // 排序后输出
        for (Map<String, Integer> m : listMap) {
            System.out.println(m);
        }
    }
}

2.List<User>排序的User.java类：

package com.tao.test;

public class User implements Comparable<User>{
    
    private int id;
    private String name;

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

    public String getName() {
        return name;
    }

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

    public int getId() {
        return id;
    }

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

    @Override
    public int compareTo(User o) {
        return this.id - o.getId();//id升序排序
    }

}

3.运行截图