遍历Map的两种方法(有排序)

初始化一个map

Map<String, String> map = new HashMap<String, String>();map.put("1", "hell");map.put("2", "hello");map.put("3", "hel");map.put("4", "hello");

1、第一种方式，普遍使用

Set<String> keySet = map.keySet();for (String key : keySet) {     System.out.PRintln("key= " + key + " and value= " + map.get(key));}

2、第二种方式，容量大时推荐使用

Set<Map.Entry<String,String>> entySet =  map.entrySet();for (Map.Entry<String, String> entry : entySet) {System.out.println("key= " + entry.getKey() + " and value= "+ entry.getValue());}

实验发现输出的顺序是乱的，排个序吧

1、按照key值排序

首先写个排序类

private static class KeyComparator implements        Comparator<Map.Entry<String, String>> {    public int compare(Map.Entry<String, String> m,            Map.Entry<String, String> n) {        return m.getKey().compareTo(n.getKey());    }}

把数据放在list里边才可以使用

List<Map.Entry<String, String>> list = new ArrayList<Map.Entry<String, String>>();list.addAll(map.entrySet());KeyComparator kc = new KeyComparator();Collections.sort(list, kc);for (Iterator<Map.Entry<String, String>> it = list.iterator(); it        .hasNext();) {    System.out.println(it.next());}

2、按照Value值排序

private static class ValueComparator implements        Comparator<Map.Entry<String, String>> {    public int compare(Map.Entry<String, String> m,            Map.Entry<String, String> n) {        return m.getValue().compareTo(n.getValue());    }}

排序输出

list.clear();list.addAll(map.entrySet());ValueComparator vc = new ValueComparator();Collections.sort(list, vc);for (Iterator<Map.Entry<String, String>> it = list.iterator(); 　　　　it.hasNext();) {    System.out.println(it.next());}

Tips: 如有错误请指出，我会及时修改