FizzBuzz implementation using the ternary operator

At first I wasn't sure whether this code would compile correctly (but obviously it does). The reason it does is due to two independent features of Java.

The System.out.println() method has an overload that takes an Object parameter (and then calls String.valueOf() to get a string representation of the object). Every type of object in Java derives from the Object base class. So, the literal string values you are passing are actually instances of the String class, which is assignable to Object.

But what about that i at the end of the chain of conditionals? That's not a string, and an int is not an Object either (primitive types in Java are not subclasses of Object). However, Java has a feature called "boxing" where primitive values can be placed inside an object container, in this case the Integer class. The compiler automatically boxes primitive values that are passed to Object parameters.

If you were to explicitly construct and cast everything your code is roughly equivalent to:

 System.out.println( (i % 15 == 0) ? (Object) new String("FizzBuzz") : (i % 3 == 0) ? (Object) new String("Fizz") : (i % 5 == 0) ? (Object) new String("Buzz") : (Object) new Integer(i) ); 

Because you are mixing different types in the conditional operator, you may find an unexpected behaviour here. For example, the following code does not compile:

 String s = ( (i % 15 == 0) ? "FizzBuzz" : (i % 3 == 0) ? "Fizz" : (i % 5 == 0) ? "Buzz" : i ); 

The reason is that in a conditional expression a ? b : c, the types of b and c must match (or be subclasses of each other). In the above case, "Buzz" and i are different incompatible types. And in particular, i cannot be assigned to a String.

I realise that in CR we are encouraged to review the code rather than suggest alternatives but in this case there are good reviews so I hope I can be forgiven for posting alternative methods.

How about this?

enum FizzBuzz { Fizz(3), Buzz(5); final int divisor; FizzBuzz(int divisor) { // Each has a divisor. this.divisor = divisor; } public boolean useName(int n) { // Use the name if the divisor is a factor. return n % divisor == 0; } } public void test() { for (int i = 1; i < 20; i++) { StringBuilder s = new StringBuilder(); // Walk all the FizzBuzzes for (FizzBuzz fb : FizzBuzz.values()) { if (fb.useName(i)) { // Add up all possible names. s.append(fb.name()); } } if (s.length() == 0) { // No names used - use the number instead. s.append(i); } System.out.println(i + " - " + s); } } 

The sweet part of this method is that you can extend it trivially with say:

 Fizz(3), Buzz(5), Pling(7); 

and it all still works in exactly the way you would expect.

This is essentially coding the algorithm and the data separately.