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