CSC207 Course Notes - Fizz Buzz

Let's start off our exploration of Java with a classic programming challenge, Fizz Buzz!

Fizz Buzz

Fizz Buzz is a game where people sit in a circle. Counting from 1 and going around the circle, people say one of four things for a number i:

we must create different outputs based on a number we continually increment. It is a classic technical interview question. Print Let i be a number; output the following:

• If i is divisible by 3, print 'Fizz'
• If i is divisible by 5, print 'Buzz'
• If i is divisibly by 3 and 5, print 'Fizz Buzz'
• Otherwise, print the value of i

So, starting with i = 1 and counting until i = 6 we would get:

1
2
Fizz
4
Buzz
Fizz

A Java version

/**
 * Solve the FizzBuzz challenge.
 */
class FizzBuzz {

    public static void main(String[] args) {

        for (int i = 1; i < 100; i++) {

            // Find out which numbers divide i.
            boolean divisibleBy3 = i % 3 == 0;
            boolean divisibleBy5 = i % 5 == 0;

            // Print our appropriate result.
            if (divisibleBy3 && divisibleBy5) {

                System.out.println("Fizz Buzz");

            } else if (divisibleBy3) {

                System.out.println("Fizz");

            } else if (divisibleBy5) {

                System.out.println("Buzz");

            } else {

                System.out.println(i);

            }
        }
    }
}

This program (which you should run for yourself right now; open Lab1/src/FizzBuzz in the top left of this window and click the Run button) prints out the first 100 numbers of Fizz Buzz. You may never have seen Java before, but we bet you can puzzle out how it works. Take a minute and read this through and take guesses at what different pieces of the code do. For example, what's the Java version of Python's and? What's going on with that weird for loop?

The Main Function

In Python, any code that you write in a file will get run when you execute the file. This is not the case in Java. You must define a method called main in a class and tell Java ot run the file containing that class.

public static void main(String[] args)

This is the main method, the entry point of your program. You have installed Java, and it is a program that knows how to to compile and run your program — it calls method main in the file you choose to run.

Later in this course, you'll learn what all that mess means.

Rewrite this using while

You've puzzled through how Java for and if statements work. Rewrite this to use a while loop instead of a for loop.

How to test it

How do you know that it's correct? Part of the problem here is that we can't easily test this program. The iteration and the calculation are tightly coupled. If we refactored this by extracting the body of the loop into a method, we could test the calculation for several interesting numbers.

How to refactor it

Select all the lines inside the body of the loop. Don't include the for/while line or the closing brace } of the loop.

Now select menu item

Refactor —> Extract/Introduce —> Method…

Immediately, type the method name you want, maybe something like doFizzBuzz. Rerun the program to verify.

That's your first big IntelliJ trick! There are lots more.