有趣的Java 6

1. Map

        // Map 比较像 JavaScript 的动态对象
        Map<String,Object> map = new HashMap<>();
        map.put("key1","hehe");
        map.put("key2",123);
        System.out.println(map);                // {key1=hehe, key2=123}
        System.out.println(map.get("key3"));    // null

2. Collections

   List<Integer> list = Arrays.asList(1, 2, 3);
        System.out.println(Collections.max(list));  // 3

        List<Integer> list2 = new ArrayList<>();
        Collections.addAll(list2, 4, 5);
        System.out.println(list2);                   // [4, 5]

        Collections.swap(list2,0,1);
        System.out.println(list2);                   // [5, 4]