面試那些奇奇怪怪的問題

int a=0;
        int b=0;
        a=a++;
        b=a++;
        System.out.println(a);
        System.out.println(b);
           

1

HashMap<Object, Object> map = new HashMap<>();
        System.out.println(map.get(null));
        map.put(null, null);
        System.out.println(map.get(null));
           

null

null