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Swap Two Numbers Using a Third Variable in Java

beginner· Basics & I/O · Variables

Problem

Swapping two variables means exchanging their values, so each ends up holding what the other used to have.

Given two integers, swap their values using a temporary third variable.

Input

a=5, b=10

Output

a=10, b=5

Java Program

Java

public class SwapUsingThirdVariable {
    public static void main(String[] args) {
        int a = 5;
        int b = 10;

        int temp = a; // save a's value before it's overwritten
        a = b;
        b = temp;

        System.out.println("a=" + a + ", b=" + b);
    }
}

▶ Run Code

Output

a=10, b=5

Core Logic

A temporary variable holds one value safely while it's overwritten, so nothing is lost during the exchange.

How It Works

1temp = a saves a's original value (5) before it gets overwritten.
2a = b copies b's value (10) into a, overwriting a's original 5.
3b = temp copies the saved original value (5) from temp into b, completing the swap.

Starting with a=5, b=10: temp becomes 5, then a becomes 10, then b becomes 5 — ending at a=10, b=5.

💡

Key Point: Without temp, the line a = b would overwrite a's value before it's ever saved, permanently losing the original number.

Key Concepts

temporary variablevariable assignment

Approach 2: Swap Using a Helper Method

Java

public class SwapUsingMethod {
    static void swap(int[] values) {
        int temp = values[0];
        values[0] = values[1];
        values[1] = temp;
    }

    public static void main(String[] args) {
        int[] values = {5, 10};
        swap(values); // shared array, so the change is visible here too
        System.out.println("a=" + values[0] + ", b=" + values[1]);
    }
}

▶ Run Code

Output

a=10, b=5

Core Logic

Java passes primitive int arguments by value, so a method can't swap two plain int parameters directly — wrapping them in an array lets a helper method mutate shared storage instead.

How It Works

1The two values are stored in a shared int[] array instead of separate variables.
2swap(values) receives a reference to that same array, not a copy of its contents.
3Inside swap, the same temp-variable technique swaps values[0] and values[1] — and because the array is shared, the change is visible back in main.

Calling swap({5, 10}) mutates the array in place, so after the call values[0] is 10 and values[1] is 5.

💡

Key Point: This is why swap helper methods in Java take arrays, lists, or wrapper objects instead of plain int parameters — a swap(int a, int b) method would have no effect outside its own scope.