please help me

I need two methods that add and subtract two very large numbers in java created in a class called number and it runs on the demo below class below.

Please don't use parseInt or BigIntger, they are not allowed.

Thank you so much

public class demoClass {

public static void main(String[] args) {

number num1; //number is class that we need to create to the add and subtract methods

num1 = new number("11111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111");

number num2; //number is class that we need to create to the add and subtract methods

num2 = new number("22222222222222222222222222222222222222222222222222222222222222222222222222222222");

number sum = num1.add(num2);

number minus = num1.subtract(num2);

}

}