FizzBuzz with Lambda Expressions in Java

Question

I wanted to create a FizzBuzz in Java that is supposed to be open for extension.

So the initial problem is the good old, if divisible by 3 print fizz, if divisible by 5 print buzz, if divisible by both print fizzbuzz, otherwise print the number itself.

But I want to be able to change the numbers that we test against (3 and 5 can become 4 and 6) and the words we print (fizz and buzz may be come foo and bar). And there may be new ones added, such as 7, qux..

Here is what I came up with, any suggestions are welcome:

import java.util.*;
import java.util.function.Function;
import java.util.function.IntPredicate;

class App {
    public static void main(String[] args) {
        Function<Integer, IntPredicate> divisibilityPredicateBuilder 
            = isDivisibleBy -> x -> x % isDivisibleBy == 0;

        final Map<Integer, String> fizzersBuzzers = new HashMap<>();
        fizzersBuzzers.put(3, "fizz");
        fizzersBuzzers.put(5, "buzz");

        for (int i = 1; i < 101; i++) {
            String fizzBuzz = "";

            for (Integer fizzerBuzzer : fizzersBuzzers.keySet()) {
                if (divisibilityPredicateBuilder.apply(fizzerBuzzer).test(i)) {
                    fizzBuzz += fizzersBuzzers.get(fizzerBuzzer);
                    fizzBuzz += " ";
                }
            }

            if (fizzBuzz.isEmpty()) {
                fizzBuzz = String.valueOf(i);
            }

            System.out.println(fizzBuzz.trim());
        }
    }
}

Answer 1

You used a HashMap, where the iteration order is arbitrary. There is no guarantee whether you'll get "fizz buzz" or "buzz fizz"!