Map 的遍历方法

  Map<String, String> map = new HashMap<String, String>();    map.put("key1", "value1");    map.put("key2", "value2");    map.put("key3", "value3");    //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    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());    }    //第三种：推荐，尤其是容量大时</span>    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);    }