你不知道的Map家族中的那些冷门容器

  public static void main(String[] args) {
        String a = new String("a");
        String b = new String("b");
        Map weakmap = new WeakHashMap();
        weakmap.put(a, "aaa");
        weakmap.put(b, "bbb");
        a = null;
        b = null;
        // 进行gc
        System.gc();
        Iterator j = weakmap.entrySet().iterator();
        while (j.hasNext()) {
            Map.Entry en = (Map.Entry) j.next();
            System.out.println("weakmap:" + en.getKey() + ":" + en.getValue());
        }
    }

public static void main(String[] args) {
        // 构造函数传入类型
        Map<DayOfWeek, String> map = new EnumMap<>(DayOfWeek.class);
        map.put(DayOfWeek.MONDAY, "星期一");
        map.put(DayOfWeek.TUESDAY, "星期二");
        map.put(DayOfWeek.WEDNESDAY, "星期三");
        map.put(DayOfWeek.THURSDAY, "星期四");
        map.put(DayOfWeek.FRIDAY, "星期五");
        map.put(DayOfWeek.SATURDAY, "星期六");
        map.put(DayOfWeek.SUNDAY, "星期日");
        System.out.println(map);
        System.out.println(map.get(DayOfWeek.MONDAY));
    }

    enum DayOfWeek {
        MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
    }

 public V put(K key, V value) {
        // 对枚举类型进行检查，看key和构造函数传入的class类型是否一致
        typeCheck(key);
        // 枚举的顺序
        int index = key.ordinal();
        // 原来位置的值
        Object oldValue = vals[index];
        // 设置值
        vals[index] = maskNull(value);
        if (oldValue == null)
            size++;
        return unmaskNull(oldValue);
    }

public static void main(String[] args) {
        // hashMap
        Map<Integer, String> hashMap = new HashMap<>();
        // identityHashMap
        Map<Integer, String> identityHashMap = new IdentityHashMap<>();

        hashMap.put(new Integer(200), "a");
        hashMap.put(new Integer(200), "b");
        identityHashMap.put(new Integer(200), "a");
        identityHashMap.put(new Integer(200), "b");

        //遍历hashmap
        System.out.println("hashmap 结果：");
        hashMap.forEach((key, value) -> {
            System.out.println("key = " + key + ", value = " + value);
        });

        //遍历hashmap
        System.out.println("identityHashMap 结果：");
        identityHashMap.forEach((key, value) -> {
            System.out.println("key = " + key + ", value = " + value);
        });

    }