Java HashMap是按键排序的

import java.util.HashMap;

public class testMain {

/**
* @param args
*/
public static void main(String[] args) {
new testMain();
}

public testMain(){
HashMap<Integer, String> arr = new HashMap<Integer, String>();
arr.put(3,"c");
arr.put(2,"b");
arr.put(4,"d");
arr.put(1,"a");

for(int key: arr.keySet())
System.out.println(key+"=>"+arr.get(key));
}
}

1=>a
2=>b
3=>c
4=>d