Map ,HashMap , TreeMap , TreeMap 默认排序

import java.util.HashMap;  
import java.util.LinkedHashMap;  
import java.util.Map;  
import java.util.TreeMap;  
  
public class Test {  
public static void main(String[] args) {  
    Map tree = new TreeMap();  
    Map linked = new LinkedHashMap();  
    Map hash = new HashMap();  
    System.out.println("tree :"+buildMap(tree));  
    System.out.println("link :"+buildMap(linked));  
    System.out.println("hash :"+buildMap(hash));  
}  
private static Map buildMap(Map map){  
    map.put("0", "a");  
    map.put("e", "b");  
    map.put("4", "s");  
    map.put("3", "c");  
    return map;  
}  
}  

输出结果： 

tree :{0=a, 3=c, 4=s, e=b}  
link :{0=a, e=b, 4=s, 3=c}  
hash :{3=c, 0=a, 4=s, e=b}  

由此可见： 
HashMap是按照HashCode 排序，莫名其妙的顺序。 
TreeMap是按照自身的顺序排序，比如数字的话，按照数字升序，ascII等。 
LinkedHashMap是按照先进先出的顺序。