使用java對List排序

1、以List中的一個字段【thousandrate】，從大到小進行排序：

排序List：mapList

調用函數：Collections.sort（）

Collections.sort(mapList, new Comparator<Map<String, Object>>() {
            @Override
            public int compare(Map<String, Object> o1, Map<String, Object> o2) {

                Integer v1 = Integer.valueOf(o1.get("thousandrate").toString());
                Integer v2 = Integer.valueOf(o2.get("thousandrate").toString());
                if (v2 != null){
                    return v2.compareTo(v1);
                }
                return 0;
            }
        });

 2、List排序函數：sort()

傳參，調用以下函數，結果就是以“thousandrate”從大到小排序

排序List：mapList

調用方法：直接調用 sort(mapList);

重寫sort()方法：

public void sort(List<Map<String, Object>> list){
        Collections.sort(list, new Comparator<Map<String, Object>>() {
            @Override
            public int compare(Map<String, Object> m1, Map<String, Object> m2) {
                Integer v1 = Integer.valueOf(m1.get("thousandrate").toString());
                Integer v2 = Integer.valueOf(m2.get("thousandrate").toString());
                if (v1 != null){
                    return v1.compareTo(v2);
                }
                return 0;
            }
        });
    }

 例子：

package com.mooc.springboordemo1.springboordemo1;

import java.net.SocketException;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;


public class MapSort {
    public static void main(String[] args) throws UnknownHostException, SocketException {

        List<Map<String, Object>> listResult = new ArrayList<Map<String, Object>>();
        Map<String, Object> map1 = new LinkedHashMap<String, Object>();
        map1.put("count", 2);
        map1.put("name", "abc");
        map1.put("key", "acv");
        listResult.add(map1);
        Map<String, Object> map2 = new LinkedHashMap<String, Object>();
        map2.put("count", 3);
        map2.put("name", "bbc");
        map2.put("key", "bcv");
        listResult.add(map2);
        Map<String, Object> map3 = new LinkedHashMap<String, Object>();
        map3.put("count", 1);
        map3.put("name", "cbc");
        map3.put("key", "ccv");
        listResult.add(map3);
        Map<String, Object> map4 = new LinkedHashMap<String, Object>();
        map4.put("count", 4);
        map4.put("name", "cbc");
        map4.put("key", "ccv");
        listResult.add(map4);

        System.out.println("排序前：");
        for (Map<String, Object> map : listResult) {
            System.out.println("count:"+map.get("count")+" name:"+map.get("name")+" key:"+map.get("key"));
        }

        Collections.sort(listResult, new MapComparatorDesc());

        System.out.println("降序：");
        for (Map<String, Object> map : listResult) {
            System.out.println("count:"+map.get("count")+" name:"+map.get("name")+" key:"+map.get("key"));
        }

        Collections.sort(listResult, new MapComparatorAsc());

        System.out.println("升序：");
        for (Map<String, Object> map : listResult) {
            System.out.println("count:"+map.get("count")+" name:"+map.get("name")+" key:"+map.get("key"));
        }
    }
    static class MapComparatorDesc implements Comparator<Map<String, Object>> {
        @Override
        public int compare(Map<String, Object> m1, Map<String, Object> m2) {
            Integer v1 = Integer.valueOf(m1.get("count").toString());
            Integer v2 = Integer.valueOf(m2.get("count").toString());
            if (v2 != null) {
                return v2.compareTo(v1);
            }
            return 0;
        }

    }
    static class MapComparatorAsc implements Comparator<Map<String, Object>> {
        @Override
        public int compare(Map<String, Object> m1, Map<String, Object> m2) {
            Integer v1 = Integer.valueOf(m1.get("count").toString());
            Integer v2 = Integer.valueOf(m2.get("count").toString());
            if(v1 != null){
                return v1.compareTo(v2);
            }
            return 0;
        }

    }
}

/*運行結果
排序前：
count:2 name:abc key:acv
count:3 name:bbc key:bcv
count:1 name:cbc key:ccv
count:4 name:cbc key:ccv
降序：
count:4 name:cbc key:ccv
count:3 name:bbc key:bcv
count:2 name:abc key:acv
count:1 name:cbc key:ccv
升序：
count:1 name:cbc key:ccv
count:2 name:abc key:acv
count:3 name:bbc key:bcv
count:4 name:cbc key:ccv
*/