java-集合操作

遍历Map的四种方法

public static void main(String[] args) {

Map<String, String> map = new HashMap<String, String>();

map.put("1", "value1");

map.put("2", "value2");

map.put("3", "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

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);

}

}