Collide two strings on purpose

import java.util.*;

/**
 * Warm-up: collisions are normal.
 *
 * "Aa" and "BB" hash to the same int. That is not a JDK bug, and String is not
 * badly written — there are more possible Strings than there are int values,
 * so some pairs must collide.
 *
 * Run this, then do the two TODOs.
 */
public class Starter {

    public static void main(String[] args) {
        System.out.println("\"Aa\".hashCode() = " + "Aa".hashCode());
        System.out.println("\"BB\".hashCode() = " + "BB".hashCode());
        System.out.println("\"Aa\".equals(\"BB\") = " + "Aa".equals("BB"));

        // TODO 1: find another colliding pair and print it.
        //
        // Hint: String.hashCode() is s[0]*31^(n-1) + s[1]*31^(n-2) + ...
        // For two characters that is c0 * 31 + c1. So raising the first
        // character by one and lowering the second by 31 lands on the same
        // total. Start from "Aa" and work out the next pair by hand.

        // TODO 2: put both strings of your pair into a HashSet and print its
        // size. Predict the number before you run it.
        //
        // If collisions broke maps, the set could not hold both. Does it?
    }
}