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[Java教程]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