hashmap排序

Map<String, Integer> map = new HashMap<String, Integer>();
map.put("d", 2);
map.put("c", 1);
map.put("b", 1);
map.put("a", 3);

List<Map.Entry<String, Integer>> infoIds =
    new ArrayList<Map.Entry<String, Integer>>(map.entrySet());

//排序前
for (int i = 0; i < infoIds.size(); i++) {
    String id = infoIds.get(i).toString();
    System.out.println(id);
}
//d= 2
//c =1
//b =1
//a= 3

//排序
Collections.sort(infoIds, new Comparator<Map.Entry<String, Integer>>() {  
    public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2) {     
        //return (o2.getValue() - o1.getValue());
        return (o1.getKey()).toString().compareTo(o2.getKey());//getKey()是根据键排序，getValue()是根据值来排序
    }
});

//排序后
for (int i = 0; i < infoIds.size(); i++) {
    String id = infoIds.get(i).toString();
    System.out.println(id);
}
//根据key排序
//a =3
//b =1
//c =1
//d =2
//根据value排序
//a =3
//d =2
//b= 1
//c= 1