How to save the previous result

bhxbr922 :

I have a task

Create a class Math with methods: int calculate (int a, int b) - the operation itself and int returnPrev () - returns the previous calculated result.

Create class Addition to represent addition operations. Override the methods. I've created abstract class Math

    abstract class Math {
        abstract int calculate(int a,int b);
        abstract int returnPrev();
    }


    public class Addition extends Math {
        int result;
        int prevresult;


        @Override
        int calculate(int a, int b) {
           result = a + b;
            return result   }
        @Override
        int returnPrevious() {
         }
    }

For me is unclear how should i create a method returnPrevious ?? I do not understand how should i save the first result.

For any explanation would be very grateful

Arvind Kumar Avinash :

Do not use a name which OOTB e.g you should use MyMath to avoid conflict with OOTB Math.
It's better to declare MyMath as in interface. Note that multiple interfaces can be implemented by a class but only one class can be extended.
Assign the value of result to prevresult before putting the value of new calculation into it.


interface MyMath {
    public int calculate(int a, int b);
    public int returnPrev();
}

class Addition implements MyMath {
    int result;
    int prevresult;

    @Override
    public int calculate(int a, int b) {
        prevresult = result;
        result = a + b;
        return result;
    }

    @Override
    public int returnPrev() {
        return prevresult;
    }
}

public class Demo {

    public static void main(String[] args) {
        Addition addition = new Addition();
        System.out.println(addition.calculate(10, 20));
        System.out.println(addition.returnPrev());
        System.out.println(addition.calculate(20, 30));
        System.out.println(addition.returnPrev());
    }
}

Output: