【Java】java 遍历map对象的四种方式

1. 使用Map.Entry遍历

Map<String, ArrayList<String>> map = new HashMap<>();for (Map.Entry<String, ArrayList<String>> entry : map.entrySet()) {     String key = entry.getKey();     ArrayList<String> item = entry.getValue();      // ....}

2. for-each 循环遍历keys和values

for (String s : map.keySet()) {    // ...}for (ArrayList<String> e : map.values()) {    // ...}

3. 使用Iterator

Map<Integer, Integer> map = new HashMap<>();    Iterator<Map.Entry<Integer, Integer>> entries = map.entrySet().iterator();    while (entries.hasNext()) {     Map.Entry<Integer, Integer> entry = entries.next();     // ...}  

4. 二次取值

Map<Integer, Integer> map = new HashMap<>();    for (Integer key : map.keySet()) {        Integer value = map.get(key);        // ...}