Java中Map集合的遍历方式

方法一：在for-each循环中使用entries来遍历

Map<Integer, Integer> map = new HashMap<Integer, Integer>();  
  
for (Map.Entry<Integer, Integer> entry : map.entrySet()) {  
  
    System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());  
  
}  

方法二：使用Iterator遍历

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

Iterator<Map.Entry<Integer, Integer>> entries = map.entrySet().iterator();

while (entries.hasNext()) {

    Map.Entry<Integer, Integer> entry = entries.next();

    System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());

}

该方法还设计到一种设计模式，即迭代模式。该方法可以在遍历时调用iterator.remove()来删除entries。

也可以不加入泛型：

Map map = new HashMap();

Iterator entries = map.entrySet().iterator();

while (entries.hasNext()) {

    Map.Entry entry = (Map.Entry) entries.next();

    Integer key = (Integer)entry.getKey();

    Integer value = (Integer)entry.getValue();

    System.out.println("Key = " + key + ", Value = " + value);

}

方法三 通过键集合遍历值

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

for (Integer key : map.keySet()) {

    Integer value = map.get(key);

    System.out.println("Key = " + key + ", Value = " + value);

}

该方法效率很低，不推荐使用

方法四 values()方法

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


for (Integer key : map.keySet()) {

    System.out.println("Key = " + key);

}
 9 
for (Integer value : map.values()) {

    System.out.println("Value = " + value);

}