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遍历Map的两种方法(有排序)


 

 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());
}