map常用遍历方式

1.最常见的遍历

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

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

2.foreach分别获取key或value，性能比1高大约10%

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

for (Integer key : map.keySet()) {
      System.out.println("key = " + key);
}

for (Integer value : map.values()) {
      System.out.println("key = " + value);
}

3.利用iterator获取key和value，好处是在遍历时可用iterator.remove()删除entryIterator，性能同2

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

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

while(entryIterator.hasNext()) {
        Map.Entry<Integer, Integer> entry = entryIterator.next();
        System.out.println("key = " + entry.getKey() +", value = " + entry.getValue());
}