How can I only use 2 variables in Java as with the Python code?

Can this Python code also be written in Java code? :

def gcd(a, b):
    # Return greatest common divisor using Euclid's Algorithm.
    while b:
        a, b = b, a % b
    return a

print (gcd(210, 45))

This is what I've so far in Java code:

private static int gcd(int p, int q) {
    // Return greatest common divisor using Euclid's Algorithm.
    int temp;
    while (q != 0) {
        temp = q;
        q = p % q;
        p = temp;
    }
    return p;
}

System.out.println(gcd(210, 45));

As you can see the Java code uses 3 variables whereas the Python code only uses 2 variables. I also want to use only 2 variables in the Java code and I want to keep the while loop and I don't want to use recursion.

Also why does Java need 1 more variable than the Python code? Except for the fact that the Python code uses a tuple.

Two variables but you still have to swap.

public static int gcd(int r, int s) {
	while (s != 0) {
		r %= s;
        // swap them
		r ^= s;
		s ^= r;
		r ^= s;
	}
	return r;
}

Another possibility (but it wouldn't be Java) is to write a routine in byte code, store it in a byte[] array and execute it as a Java method. If using the internal stack is okay as it is in Python, then it should be okay here.

The reason for the difference is that Python has a tuple creation/decomposition feature, and Java does not.

As other answers have mentioned, you can do an integer swap with either xor or addition/subtraction. However, I suspect that for performance platforms like C or Rust, this is a false economy, and this hack will not speed things up or decrease resource usage. (If you're just in it for the challenge, though, it's legit, and probably the only solution)

Also, I don't think Java permits this trick for more general object references.

How about doing two steps in each loop iteration and not swapping at all?

private static int gcd(int p, int q) {
    // Return greatest common divisor using Euclid's Algorithm.
    while (q != 0) {
        p %= q;
        if (p == 0)
           return q;
        q %= p;
    }
    return p;
}

Correct me If I'm wrong but, you can also do gcd operation using 2 variables in java.

private static int gcd(int p, int q) {
    // Return greatest common divisor using Euclid's Algorithm.
    int temp;
    while (p != q) {
        if(p > q)
            p = p - q;
        else
            q = q - p;
    }
    return q;
}

Python might be adding some synthetic sugar on top of the "exclusive or" operator. This is a bitwise operation to swap values of two different variables without using a temporary variable.

See Java example below:

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-java -->

a = a^b;
b = a^b;
a = a^b;

<!-- end snippet -->

See https://en.wikipedia.org/wiki/XOR_swap_algorithm

Aside from the given examples, there is a well known algorithm to swap two integer variables a and b without the use of a third variable:

// given: two int-variables a and b
a += b;
b = a - b;
a -= b
// result: a and b have been swapped

If we now first calculate a % b and assign it to a, all that is left to do is to swap a and b:

// given: two int-variables a and b
a = a % b;
a += b;
b = a - b;
a -= b
// result: the new value of a is b, while the new value of b is a % b

This even works if the addition a + b overflows, since it is reversed by the subtractions.

As an aside: I see this as a code golf. Unless one is under heavy memory constraint, I would not advice to use this solution.