Java TreeMap升序|降序排列和按照value进行排序的案例

import java.util.Comparator;
import java.util.TreeMap;
public class Main {
  public static void main(String[] args) {
    TreeMap<Integer,Integer> map1 = new TreeMap<Integer,Integer>(); //默认的TreeMap升序排列
    TreeMap<Integer,Integer> map2= new TreeMap<Integer,Integer>(new Comparator<Integer>(){
       /* 
       * int compare(Object o1, Object o2) 返回一个基本类型的整型， 
       * 返回负数表示：o1 小于o2， 
       * 返回0 表示：o1和o2相等， 
       * 返回正数表示：o1大于o2。 
       */ 
      public int compare(Integer a,Integer b){
        return b-a;      
      }
      });
    map2.put(1,2);
    map2.put(2,4);
    map2.put(7, 1);
    map2.put(5,2);
    System.out.println("Map2="+map2); 
    
    map1.put(1,2);
    map1.put(2,4);
    map1.put(7, 1);
    map1.put(5,2);
    System.out.println("map1="+map1);
  }
}

public static void sortByValue() {
    Map<String,String> map = new TreeMap<String,String>();
    map.put("a", "dddd");
    map.put("d", "aaaa");
    map.put("b", "cccc");
    map.put("c", "bbbb");
    
    List<Entry<String, String>> list = new ArrayList<Entry<String, String>>(map.entrySet());
    
    Collections.sort(list,new Comparator<Map.Entry<String,String>>() {
      //升序排序
      public int compare(Entry<String, String> o1, Entry<String, String> o2) {
        return o1.getValue().compareTo(o2.getValue());
      }
    });
    
    for (Entry<String, String> e: list) {
      System.out.println(e.getKey()+":"+e.getValue());
    }
  }

public class MapSortDemo {
  public static void main(String[] args) {
    Map<String, String> map = new TreeMap<String, String>();
    map.put("KFC", "kfc");
    map.put("WNBA", "wnba");
    map.put("NBA", "nba");
    map.put("CBA", "cba");
    Map<String, String> resultMap = sortMapByKey(map); //按Key进行排序
//   Map<String, String> resultMap = sortMapByValue(map); //按Value进行排序
    for (Map.Entry<String, String> entry : resultMap.entrySet()) {
      System.out.println(entry.getKey() + " " + entry.getValue());
    }
  }
  /**
   * 使用 Map按value进行排序
   * @param map
   * @return
   */
  public static Map<String, String> sortMapByValue(Map<String, String> oriMap) {
    if (oriMap == null || oriMap.isEmpty()) {
      return null;
    }
    Map<String, String> sortedMap = new LinkedHashMap<String, String>();
    List<Map.Entry<String, String>> entryList = new ArrayList<Map.Entry<String, String>>(
        oriMap.entrySet());
    Collections.sort(entryList, new MapValueComparator());
    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;
  }
}

//比较器
class MapValueComparator implements Comparator<Map.Entry<String, String>> {
  @Override
  public int compare(Entry<String, String> me1, Entry<String, String> me2) {
    return me1.getValue().compareTo(me2.getValue());
  }
}

public class TreeMapTest {
  public static void main(String[] args) {
    Map<String, String> map = new TreeMap<String, String>();
    map.put("a", "ddddd");
    map.put("c", "bbbbb");
    map.put("d", "aaaaa");
    map.put("b", "ccccc");
    //这里将map.entrySet()转换成list
    List<Map.Entry<String,String>> list = new ArrayList<Map.Entry<String,String>>(map.entrySet());
    //然后通过比较器来实现排序
    Collections.sort(list,new Comparator<Map.Entry<String,String>>() {
      //升序排序
      public int compare(Entry<String, String> o1,
          Entry<String, String> o2) {
        return o1.getValue().compareTo(o2.getValue());
      }
    });
    for(Map.Entry<String,String> mapping:list){ 
        System.out.println(mapping.getKey()+":"+mapping.getValue()); 
     } 
  }
}