How to exit return loop in java?

Question

I'm not new to programming per se, I have studied C# for quite a while now, but I haven't really done a lot of exercises by myself, I'm just now starting with java because I want to do Android apps and to test my newly acquired knowledge I wanted to do a basic console calculator, here's what I got so far:

package calculatorSource;

import java.util.*;

public class calculatorJava {
    private static Scanner input;

    public static void main(String[] args) {
        System.out.println("Select an operation");

        String choice = null;
        input = new Scanner(System.in);

        while(choice == null) {
            System.out.println("Type 'a' for adition, 's' for subtraction, 'm' for multiplication," + " 'd' for division, or 'mo' for module.");
            choice = input.next();
        }

        while(choice != null) {
            if(choice.equals("a")) {
                System.out.println(adition(0, 0));
                choice = null;
            } else if(choice.equals("s")) {
                System.out.println(subtraction(0, 0));
                choice = null;
            } else if(choice.equals("m")) {
                System.out.println(multiplication(0, 0));
                choice = null;
            } else if(choice.equals("d")) {
                System.out.println(division(0, 0));
                choice = null;
            } else if(choice.equals("mo")) {
                System.out.println(module(0, 0));
                choice = null;
            } else {
                System.out.println("Option not available, please try again.");
                choice = null;
            }
        }
    }

    public static float adition(float n1, float n2) {
        input = new Scanner(System.in);

        float result;

        System.out.println("Enter first number:");
        n1 = input.nextFloat();

        System.out.println("Enter second number:");
        n2 = input.nextFloat();

        result = n1 + n2;

        System.out.println("Result is: " + result);

        return adition(result, result);
    }

    public static float subtraction(float n1, float n2) {
        input = new Scanner(System.in);

        float result;

        System.out.println("Enter first number:");
        n1 = input.nextFloat();

        System.out.println("Enter second number:");
        n2 = input.nextFloat();

        result = n1 - n2;

        System.out.println("Result is: " + result);

        return subtraction(result, result);
    }

    public static float multiplication(float n1, float n2) {
        input = new Scanner(System.in);

        float result;

        System.out.println("Enter first number:");
        n1 = input.nextFloat();

        System.out.println("Enter second number:");
        n2 = input.nextFloat();

        result = n1 * n2;

        System.out.println("Result is: " + result);

        return multiplication(result, result);
    }

    public static float division(float n1, float n2) {
        input = new Scanner(System.in);

        float result;

        System.out.println("Enter first number:");
        n1 = input.nextFloat();

        System.out.println("Enter second number:");
        n2 = input.nextFloat();

        result = n1 / n2;

        System.out.println("Result is: " + result);

        return division(result, result);
    }

    public static float module(float n1, float n2) {
        input = new Scanner(System.in);

        float result;

        System.out.println("Enter first number:");
        n1 = input.nextFloat();

        System.out.println("Enter second number:");
        n2 = input.nextFloat();

        result = n1 % n2;

        System.out.println("Result is: " + result);

        return module(result, result);
    }
}

I know it probably is not the best or more efficient calculator out there, but as I said, I just started with java and this is pretty much all I know so far, the program works, as I can make an addition, a division or whatever else I choose, but right after that I want it to give me the option of selecting a different operation, I put the "choice = null" right after the return but it doesn't not seems to be working, I've tried several stuff to this point, but I'm starting to think I may have misunderstood what return actually does, so I thought it would be better to turn to you guys for help.

Any advice is appreciated, thanks!

Answer 1

Instead of

return adition(result, result);

in your adition method, return result.

Otherwise you're just going to repeat the same method until the stack overflows. (Same for other methods also).

---

Your while (choice != null) { loop isn't necessary, as you always set choice = null;. Since you also don't otherwise change the value of choice in that loop, you may as well just remove the loop.

---

There is no point in passing parameters into the adition (etc) methods, since you always overwrite them. Just declare them as local variables in those methods:

public static float adition() {  // No parameters
    // ...
    float n1 = input.nextFloat();
    // ... 
    float n2 = input.nextFloat();

Answer 2

You are recursively calling all methods infinitely. choice = null is ok. it will terminate if you will correct your code :
Instead of

MethodaName(result, result);

just write

return result; 

Also you need not pass any parameters if taking input from user in method itself.