map 几种遍历方法

ublic static void main(String[] args) {
Map<String, String> map = new HashMap<String, String>();
        map.put("无邪", 21);
        map.put("胖子", 22);
        map.put("张起灵", 23);
        map.put("三叔", 24);
//第一种：普遍使用，二次取值
System.out.println("通过Map.keySet遍历key和value：");
for (String key : map.keySet()) {
System.out.println("key= "+ key + " and value= " + map.get(key));
}

//第二种

        Iterator it = map.keySet().iterator();
        Object key;
        Object value;
        while(it.hasNext()){
            key = it.next();
            value = map.get(key);
            System.out.println(key+":"+value);
        }
//第三种
System.out.println("通过Map.entrySet使用iterator遍历key和value：");
Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();
while (it.hasNext()) {
Map.Entry<String, String> entry = it.next();
System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
}

int size = map.size();
Set keysSet = map.keySet();
Iterator iterator = keysSet.iterator();
while(iterator.hasNext()) {
Object key = iterator.next();//key
Object value = map.get(key);//value
}

推荐，尤其是容量大时
System.out.println("通过Map.entrySet遍历key和value");
for (Map.Entry<String, String> entry : map.entrySet()) {
System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
}

//第四种
System.out.println("通过Map.values()遍历所有的value，但不能遍历key");
  for (String v : map.values()) {
   System.out.println("value= " + v);
  }
}

//灵活性很强

 public static void workByEntry(Map<String, Student> map) {
        Set<Map.Entry<String, Student>> set = map.entrySet();
        for (Iterator<Map.Entry<String, Student>> it = set.iterator(); it.hasNext();) {
            Map.Entry<String, Student> entry = (Map.Entry<String, Student>) it.next();
            System.out.println(entry.getKey() + "--->" + entry.getValue());
        }
}