/**
* 按key 升序排序，並輸出結果
*/
public static void testSortByKey(){
		Map<String, String> map = new HashMap<String, String>();
	        map.put(2+"", "B");
	        map.put(4+"", "D");
	        map.put(3+"", "C");
	        map.put(1+"", "A");
	    
		List<Map.Entry<String, String>> list = new ArrayList<Map.Entry<String, String>>(map.entrySet());
		//排序前
		for (int i = 0; i < list.size(); i++) {
		    String id = list.get(i).toString();
		    System.out.println(id);
		}

		//排序
		Collections.sort(list, new Comparator<Map.Entry<String, String>>() {   
		    public int compare(Map.Entry<String, String> o1, Map.Entry<String, String> o2) {      
		        return (o1.getKey()).toString().compareTo(o2.getKey());
		    }
		}); 

		//排序後
		for (int i = 0; i < list.size(); i++) {
		    String id = list.get(i).toString();
		    System.out.println(id);
		}
}
 

測試結果：

按Key排序前：

3=C
2=B
1=A
4=D
按key排序後：
1=A
2=B
3=C
4=D