java change an Integer in an external method and have it affect original method

Question

I'm writing some code for an exercise of a book I'm currently working through on my own and I stumbled over a problem while rewriting some working code into something more readable.

The Problem

I have method A which calls method B, passing it an int value (e.g. int value = 5). I want B to look at the int value and if it is >0, decrement it by 1 (e.g.: int value = 4) and return a boolean true if int value was > 0. However I also want the change of the int value in B to affect the original int value in A. Since this does not work in java with primitives, I thought my problem would be solved here if I passed an Integer.

Example Code

public class Test {
    private static boolean isRemainder0(Integer remainder) {
        boolean is0 = true;
        if (remainder.intValue() > 0) {
            remainder = remainder.intValue() - 1;
            is0 = false;
        }
        return is0;
    }

    public static void main(String[] args) {
        Integer remainder = 5;

        System.out.println(remainder);
        System.out.println(isRemainder0(remainder));
        System.out.println(remainder);
    }
}

What I would want is for this to return 5 - false - 4. What this does return:

5
false
5

Why this does not work

Apparently if you pass a variable var1 containing an object reference, you do not pass var1 but a copy var2 == var1 of it to the new method. Therefore changes to var2 in the new method do not affect var1.

The question

How do I find a way around it?

Solutions that I want to avoid

1. Using a static variable for remainder
2. Writing a custom object containing the boolean and the changed int value of "remainder"
3. Solutions requiring me to instantiate "Test"
4. Solutions requiring me to lose the return of isRemainder0

1) I want to avoid because I'm currently trying to avoid using static variables whenever possible. 2) I want to avoid because it seems to me like bad coding.

Answer 1

make a method to return the price of remainder like:

private static Integer setRemainder(Integer remainder){
    if (remainder > 0) {
        remainder = remainder - 1;
    }
    return remainder;
}

And before print add the call:

remainder = setRemainder(remainder);

Answer 2

It's also not a good design, but you can return an array:

private static Object[] isRemainder0(Integer remainder) {
    boolean is0 = true;
    if (remainder.intValue() > 0) {
        remainder = remainder.intValue() - 1;
        is0 = false;
    }
    return new Object[]{is0, remainder};
}

public static void main(String[] args) {
    Integer remainder = 5;

    System.out.println(remainder);
    Object[] result = isRemainder0(remainder);
    System.out.println(result[0]);
    remainder = (Integer)result[1];
    System.out.println(remainder);
}

As suggested by mrjink in the comment, you can use an AtomicInteger. Thanks mrjink! I also learned something new :)

private static boolean isRemainder0(AtomicInteger remainder) {
    boolean is0 = true;
    if (remainder.intValue() > 0) {
        remainder.decrementAndGet();
        is0 = false;
    }
    return is0;
}

public static void main(String[] args) {
    AtomicInteger remainder = new AtomicInteger(5);

    System.out.println(remainder);
    System.out.println(isRemainder0(remainder));
    System.out.println(remainder);
}

Answer 3

this is a solution i came up with:

public class JavaApplication1 {
static int remainder = 0;
public static void setRemainder(int value){
    remainder = value;
}
private static boolean isRemainder0() {
    boolean is0 = true;
    if (remainder > 0) {
        remainder = remainder - 1;
        is0 = false;
    }
    return is0;
}

public static void main(String[] args) {
    setRemainder(5);

    System.out.println(remainder);
    System.out.println(isRemainder0());
    System.out.println(remainder);
}

}

the solution is what you wanted to see: 5 false 4