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); // ... }