Java-装箱与拆箱

public static void main(String[] args) {

        User user = new User();
        System.out.println(user.getA());
        System.out.println(user.getB());
    }
    public static class User{
        private int a;

        private Integer b;

        public int getA() {
            return a;
        }

        public void setA(int a) {
            this.a = a;
        }

        public Integer getB() {
            return b;
        }

        public void setB(Integer b) {
            this.b = b;
        }
    }

控制台输出：