參考：

##########################################################

降序操作：按key降序

import java.util.Comparator;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
public class test {
    public static void main(String[] args) {
        Map<Double, String> map = new TreeMap<Double, String>(
                new Comparator<Double>() {
                    public int compare(Double obj1, Double obj2) {
                        // 降序排序
                        return obj2.compareTo(obj1);
                    }
                });
        map.put(2.33, "ccccc");
        map.put(2.0, "aaaaa");
        map.put(3.0, "bbbbb");
        map.put(4.0, "ddddd");
        
        Set<Double> keySet = map.keySet();
        Iterator<Double> iter = keySet.iterator();
        while (iter.hasNext()) {
            Double key = iter.next();
            System.out.println(key + ":" + map.get(key));
        }
    }
}
 

TreeMap預設是升序的，如果我們需要改變排序方式，則需要使用比較器：Comparator。Comparator可以對集合物件或者陣列進行排序的比較器介面，實現該介面的public compare(T o1,To2)方法即可實現排序，

import java.util.Comparator;

import java.util.Iterator;

import java.util.Map;

import java.util.Set;

import java.util.TreeMap;

public class TreeMapTest {

    public static void main(String[] args) {
 

        Map<String, String> map = new TreeMap<String, String>(

                new Comparator<String>() {

                    public int compare(String obj1, String obj2) {

                        // 降序排序

                        return obj2.compareTo(obj1);

                    }

                });
 

        map.put("b", "ccccc");

        map.put("d", "aaaaa");

        map.put("c", "bbbbb");

        map.put("a", "ddddd");

        Set<String> keySet = map.keySet();

        Iterator<String> iter = keySet.iterator();

        while (iter.hasNext()) {

            String key = iter.next();

            System.out.println(key + ":" + map.get(key));

        }

    }

}

按value:

上面例子是對根據TreeMap的key值來進行排序的，但是有時我們需要根據TreeMap的value來進行排序。對value排序我們就需要藉助於Collections的sort(List<T> list, Comparator<? super T> c)方法，該方法根據指定比較器產生的順序對指定列表進行排序。但是有一個前提條件，那就是所有的元素都必須能夠根據所提供的比較器來進行比較

import java.util.ArrayList;

import java.util.Collections;

import java.util.Comparator;

import java.util.List;

import java.util.Map;

import java.util.Map.Entry;

import java.util.TreeMap;

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");

        //這裡將map.entrySet()轉換成list

        List<Map.Entry<String,String>> list = new ArrayList<Map.Entry<String,String>>(map.entrySet());

        //然後通過比較器來實現排序

        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()); 

          } 

    }

}

###################################################

升序排序：按key

import java.util.Map.Entry;
import java.util.*;

public class test {
    public static void main(String[] args) {
    	HashMap<String,String> map=new HashMap<String, String>();  
    	  map.put("1","11");  
    	  map.put("2", "22");  
    	  map.put("3", "33");  
    	  for (Entry<String,String> entry: map.entrySet()) {  
    	   System.out.println("排序之前:"+entry.getKey()+" 值"+entry.getValue());  
    	     
    	  }  
    	  System.out.println("======================================================");  
    	  SortedMap<String,String> sort=new TreeMap<String,String>(map);  
    	  Set<Entry<String,String>> entry1=sort.entrySet();  
    	  Iterator<Entry<String,String>> it=entry1.iterator();  
    	  while(it.hasNext())  
    	  {  
    	   Entry<String,String> entry=it.next();  
    	   System.out.println("排序之後:"+entry.getKey()+" 值"+entry.getValue());  
    	  } 
    }
}