遍历迭代map的集中方法

 1 public static void main(String[] args) {
 2   Map<String, String> map = new HashMap<String, String>();
 3   map.put("1", "value1");
 4   map.put("2", "value2");
 5   map.put("3", "value3");
 6   
 7   //第一种：普遍使用，二次取值
 8   System.out.println("通过Map.keySet遍历key和value：");
 9   for (String key : map.keySet()) {
10    System.out.println("key= "+ key + " and value= " + map.get(key));
11   }
12   
13   //第二种
14   System.out.println("通过Map.entrySet使用iterator遍历key和value：");
15   Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();
16   while (it.hasNext()) {
17    Map.Entry<String, String> entry = it.next();
18    System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
19   }
20   
21   //第三种：推荐，尤其是容量大时
22   System.out.println("通过Map.entrySet遍历key和value");
23   for (Map.Entry<String, String> entry : map.entrySet()) {
24    System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
25   }
26 
27   //第四种
28   System.out.println("通过Map.values()遍历所有的value，但不能遍历key");
29   for (String v : map.values()) {
30    System.out.println("value= " + v);
31   }
32  }