遍历Map集合的四种方式

1. 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()); }  

2.在for-each循环中遍历keys或values

如果只需要map中的键或者值，你可以通过keySet或values来实现遍历，而不是用entrySet

//遍历map中的键  for (Integer key : map.keySet()) {      System.out.println("Key = " + key);  }  //遍历map中的值for (Integer value : map.values()) {      System.out.println("Value = " + value);}  

3.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());  }  

4.通过键找值遍历（效率低）

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);  }