Try to write swap

import java.util.*;

/**
 * Warm-up: try to write swap, and watch Java refuse.
 *
 * Everyone is told the primitive version does not work. Far fewer people have
 * actually run the OBJECT version — which is the one that settles the
 * pass-by-value argument.
 */
public class Starter {

    static void swapPrimitives(int a, int b) {
        int t = a;
        a = b;
        b = t;
    }

    static void swapObjects(StringBuilder a, StringBuilder b) {
        StringBuilder t = a;
        a = b;
        b = t;
    }

    public static void main(String[] args) {
        int x = 1, y = 2;
        swapPrimitives(x, y);
        System.out.println("primitives : x=" + x + " y=" + y + "   (expected 1, 2 — nothing swapped)");

        StringBuilder p = new StringBuilder("first");
        StringBuilder q = new StringBuilder("second");
        swapObjects(p, q);
        System.out.println("objects    : p=" + p + " q=" + q);

        // TODO 1: was the object result what you expected? If you thought
        // objects were "passed by reference", this is the line that disproves
        // it. Write down why in a comment.

        // TODO 2: make swapObjects appear to work by CHANGING THE OBJECTS
        // rather than the references. Hint: StringBuilder has setLength(0),
        // append(), and toString().
        //
        // Then answer: did you swap the variables, or swap the contents of two
        // objects the caller still points at? They are not the same thing.

        // TODO 3: write the version you would actually ship. It returns
        // something instead of using output parameters.
        //
        //     static ??? swapped(StringBuilder a, StringBuilder b)
        //
        // A record or an array both work. Pick one and say why.
    }
}