How Can You Swap Primitive Variables in Java When Parameter Passing is by Value?

Swapping Primitive Variables in Java: Overcoming Value Passing

In Java, parameter passing is inherently by value, which poses a challenge when attempting to swap primitive variables within a method. A naive implementation, such as:

<code class="java">void swap(int a, int b) {
    int temp = a;
    a = b;
    b = temp;
}</code>

will not actually modify the original variables outside the method. To address this, here are two unconventional approaches:

Return-Assign Pattern

This technique allows swapping by leveraging the ordering of operations in method calls:

<code class="java">int swap(int a, int b) {  // usage: y = swap(x, x=y);
    return a;
}</code>

When calling swap(x, x=y), the value of x will be passed into swap before the assignment to x. Thus, when a is returned and assigned to y, it effectively swaps the values of x and y.

Generic Swapper with Variadic Parameters

For a more generalized solution, a generic method can be defined that can swap any number of objects of the same type:

<code class="java"><T> T swap(T... args) {   // usage: z = swap(a, a=b, b=c, ... y=z);
    return args[0];
}</code>

Calling this method as z = swap(a, a=b, b=c) will swap the values of a, b, and c, assigning the final value to z.

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