hashmap按value排序

Posted 2023-03-26

参考技术A

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import java.util.ArrayList;

import java.util.Collections;

import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

public class SortHashMap
public static void main(String[] args)
//产生一个map并添加一些参数
Map<String, Integer> map = new HashMap<>();
map.put("ddd", 1);
map.put("aaa", 2);
map.put("bbb", 3);
map.put("ccc", 4);
List<Map.Entry<String, Integer>> list = new ArrayList<>(map.entrySet());
//将map的entryset放入list集合
// 对list进行排序，并通过Comparator传入自定义的排序规则
Collections.sort(list, new Comparator<Map.Entry<String, Integer>>()
@Override
public int compare(Entry<String, Integer> o1, Entry<String, Integer> o2)
return o1.getValue() - o2.getValue(); //重写排序规则，小于0表示升序，大于0表示降序

);
//用迭代器对list中的键值对元素进行遍历
Iterator<Map.Entry<String, Integer>> iter = list.iterator();
while (iter.hasNext())
Map.Entry<String, Integer> item = iter.next();
String key = item.getKey();
int value = item.getValue();
System.out.println("键" + key + "值" + value);

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如满意，请采纳

Java Map 按Key排序和按Value排序

package test;

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

public class MapSortDemo {

    /**
     * @param args
     */
    public static void main(String[] args) {
        Map<String, String> hMap = new HashMap<String, String>();
        hMap.put("a", "3");
        hMap.put("z", "2");
        hMap.put("b", "6");
        hMap.put("o", "9");

        System.out.println("根据key升序排序"); 
        Map<String, String> sortByKeyResultMap = sortMapByKey(hMap);    //按Key进行排序
        Iterator<Map.Entry<String, String>> sortByKeyEntries = sortByKeyResultMap.entrySet().iterator(); 
        while (sortByKeyEntries.hasNext()) { 
          Map.Entry<String, String> entry = sortByKeyEntries.next(); 
          System.out.println("Key = " + entry.getKey() + "------->Value = " + entry.getValue()); 
        }
        
        System.out.println("------------------------------"); 
        
        System.out.println("根据value降序排序"); 
        Map<String, String> sortByValueResultMap = sortMapByValue(hMap); //按Value进行排序
        Iterator<Map.Entry<String, String>> sortByValueEntries = sortByValueResultMap.entrySet().iterator(); 
        while (sortByValueEntries.hasNext()) { 
          Map.Entry<String, String> entry = sortByValueEntries.next(); 
          System.out.println("Key = " + entry.getKey() + "------->Value = " + entry.getValue()); 
        }
    }
    /**
     * 使用 Map按key进行排序
     * @param map
     * @return
     */
    public static Map<String, String> sortMapByKey(Map<String, String> map) {
        if (map == null || map.isEmpty()) {
            return null;
        }
//        Map<String, String> sortMap = new TreeMap<String, String>(new MapKeyComparator());
        Map<String, String> sortMap = new TreeMap<String, String>(new Comparator<String>() {
            public int compare(String obj1, String obj2) {
                return obj1.compareTo(obj2);//升序排序
            }
        });
        sortMap.putAll(map);
        return sortMap;
    }
    
    /**
     * 使用 Map按value进行排序
     * @param map
     * @return
     */
    public static Map<String, String> sortMapByValue(Map<String, String> map) {
        if (map == null || map.isEmpty()) {
            return null;
        }
        Map<String, String> sortedMap = new LinkedHashMap<String, String>();
        List<Map.Entry<String, String>> entryList = new ArrayList<Map.Entry<String, String>>(map.entrySet());
//        Collections.sort(entryList, new MapValueComparator());
        Collections.sort(
            entryList, 
            new Comparator<Map.Entry<String, String>>(){
                   public int compare(Entry<String, String> o1, Entry<String, String> o2) {
                       return o2.getValue().compareTo(o1.getValue());// 降序排序
                   }
            }
        );

        Iterator<Map.Entry<String, String>> iter = entryList.iterator();
        Map.Entry<String, String> tmpEntry = null;
        while (iter.hasNext()) {
            tmpEntry = iter.next();
            sortedMap.put(tmpEntry.getKey(), tmpEntry.getValue());
        }
        return sortedMap;
    }
}

根据key升序排序
Key = a------->Value = 3
Key = b------->Value = 6
Key = o------->Value = 9
Key = z------->Value = 2
------------------------------
根据value降序排序
Key = o------->Value = 9
Key = b------->Value = 6
Key = a------->Value = 3
Key = z------->Value = 2

如果想把map排序代码分离出来就添加两个类，分别为

package test;

import java.util.Comparator;

public class MapKeyComparator implements Comparator<String> {

    @Override
    public int compare(String o1, String o2) {
        return o1.compareTo(o2);
    }

}

package test;

import java.util.Comparator;
import java.util.Map;
import java.util.Map.Entry;

public class MapValueComparator implements Comparator<Map.Entry<String, String>> {

    @Override
    public int compare(Entry<String, String> o1, Entry<String, String> o2) {
        return o2.getValue().compareTo(o1.getValue());
    }

}

注意o1和o2的位置，它们在前还是在后就会变化升序和降序的顺序。

用key排序用以下代码

 

 

用value排序用以下代码