public class FizzBuzz {
    private final List<Fizzer> fizzers;

    private static class Fizzer {
        private final String name;
        private final int divisor;

        private Fizzer(String name, int divisor) {
            this.name = name;
            this.divisor = divisor;
        }
    }

    public static class Builder {
        private final List<Fizzer> fizzers = new ArrayList<>();

        public Builder add(String name, int divisor) {
            fizzers.add(new Fizzer(name, divisor));
            return this;
        }

        public FizzBuzz build() {
            return new FizzBuzz(this);
        }
    }

    private FizzBuzz(Builder builder) {
        fizzers = Collections.unmodifiableList(builder.fizzers);
    }

    public String getValue(int num) {
        String output = "";
        for (Fizzer fizzer : fizzers) {
            if (num % fizzer.divisor == 0) {
                output += fizzer.name;
            }
        }
        return output.isEmpty() ? Integer.toString(num) : output;
    }

    public static Builder builder() {
        return new Builder();
    }
}

import static java.util.stream.IntStream.rangeClosed;

class FizzBuzzDemo {
    public static void main(String[] args) {
        FizzBuzz fizzBuzz = FizzBuzz.builder().add("Fizz", 3).add("Buzz", 5).build();
        rangeClosed(1, 100).mapToObj(fizzBuzz::getValue).forEach(System.out::println);
    }
}

import org.junit.Test;

import static org.junit.Assert.assertEquals;

public class FizzBuzzTest {
    @Test
    public void test_Without_Fizzer() {
        FizzBuzz fizzBuzz = FizzBuzz.builder().build();
        assertEquals("1", fizzBuzz.getValue(1));
        assertEquals("2", fizzBuzz.getValue(2));
        assertEquals("3", fizzBuzz.getValue(3));
        assertEquals("4", fizzBuzz.getValue(4));
        assertEquals("5", fizzBuzz.getValue(5));
        assertEquals("15", fizzBuzz.getValue(15));
        assertEquals("16", fizzBuzz.getValue(16));
        assertEquals(Integer.toString(31 * 3 * 5), fizzBuzz.getValue(31 * 3 * 5));
        assertEquals(Integer.toString(31 * 3 * 5 + 1), fizzBuzz.getValue(31 * 3 * 5 + 1));
    }

    @Test
    public void test_With_Fizz() {
        FizzBuzz fizzBuzz = FizzBuzz.builder().add("Fizz", 3).build();
        assertEquals("1", fizzBuzz.getValue(1));
        assertEquals("2", fizzBuzz.getValue(2));
        assertEquals("Fizz", fizzBuzz.getValue(3));
        assertEquals("4", fizzBuzz.getValue(4));
        assertEquals("5", fizzBuzz.getValue(5));
        assertEquals("Fizz", fizzBuzz.getValue(15));
        assertEquals("16", fizzBuzz.getValue(16));
        assertEquals("Fizz", fizzBuzz.getValue(31 * 3 * 5));
        assertEquals(Integer.toString(31 * 3 * 5 + 1), fizzBuzz.getValue(31 * 3 * 5 + 1));
    }

    @Test
    public void test_With_FizzBuzz() {
        FizzBuzz fizzBuzz = FizzBuzz.builder().add("Fizz", 3).add("Buzz", 5).build();
        assertEquals("1", fizzBuzz.getValue(1));
        assertEquals("2", fizzBuzz.getValue(2));
        assertEquals("Fizz", fizzBuzz.getValue(3));
        assertEquals("4", fizzBuzz.getValue(4));
        assertEquals("Buzz", fizzBuzz.getValue(5));
        assertEquals("FizzBuzz", fizzBuzz.getValue(15));
        assertEquals("16", fizzBuzz.getValue(16));
        assertEquals("FizzBuzz", fizzBuzz.getValue(31 * 3 * 5));
        assertEquals(Integer.toString(31 * 3 * 5 + 1), fizzBuzz.getValue(31 * 3 * 5 + 1));
    }

    @Test
    public void test_With_FizzBuzzJazz() {
        FizzBuzz fizzBuzz = FizzBuzz.builder().add("Fizz", 3).add("Buzz", 5).add("Jazz", 7).build();
        assertEquals("1", fizzBuzz.getValue(1));
        assertEquals("2", fizzBuzz.getValue(2));
        assertEquals("Fizz", fizzBuzz.getValue(3));
        assertEquals("4", fizzBuzz.getValue(4));
        assertEquals("Buzz", fizzBuzz.getValue(5));
        assertEquals("FizzBuzz", fizzBuzz.getValue(15));
        assertEquals("16", fizzBuzz.getValue(16));
        assertEquals("FizzBuzz", fizzBuzz.getValue(31 * 3 * 5));
        assertEquals(Integer.toString(31 * 3 * 5 + 1), fizzBuzz.getValue(31 * 3 * 5 + 1));
        assertEquals("FizzBuzzJazz", fizzBuzz.getValue(31 * 3 * 5 * 7));
    }
}