认识Map中的TreeMap

TreeMap是map接口的一个实现,TreeMap中的key是排好序的，这是TreeMap和HashMap最大的区别。

package test;   
import java.util.HashMap;   
import java.util.TreeMap;   
  
public class TestTreeMap {   
  
        /**  
         * @param args  
         */  
        public static void main(String[] args) {   
                //HashMap是无序的   
                prt("The following is HashMap");   
                HashMap<String,Object> hashMap = new HashMap<String,Object>();   
                hashMap.put("004", new Integer(40));   
                hashMap.put("003", new Integer(30));   
                hashMap.put("001", new Integer(10));   
                hashMap.put("002", new Integer(20));   
  
                prt(hashMap);   
                  //TreeMap是有序的   
                prt("The following is TreeMap");   
                TreeMap<String,Object> treeMap = new TreeMap<String,Object>();   
                treeMap.put("004", new Integer(40));   
                treeMap.put("003", new Integer(30));   
                treeMap.put("001", new Integer(10));   
                treeMap.put("002", new Integer(20));   
  
                prt(treeMap);   
  
        }   
  
         private static void prt(Object obj) {   
                 System.out.println(obj);   
         }   
  
  
}  

输出:
The following is HashMap
{002=20, 004=40, 001=10, 003=30}
The following is TreeMap
{001=10, 002=20, 003=30, 004=40}