Recursive FizzBuzz

import static java.lang.System.out;

Simple two-liner:

static void f(int a, int z) {
	out.println(a % 15 < 1 ? "FizzBuzz" : a % 3 < 1 ? "Fizz" : a % 5 < 1 ? "Buzz" : a);
	if (a < z) f(1 + a, z);
}

Without using the literal “FizzBuzz”:

static void g(int a, int z) {
  int x = 0;
  if (a % 3 < 1) { out.print("Fizz"); ++x; }
  if (a % 5 < 1) { out.print("Buzz"); ++x; }
  if (x < 1) out.print(a);
  out.println();
  if (a < z) g(1 + a, z);
}

Note that I use x<1 instead of x==0 to save a single character.

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Y Combinator in Java 8

The Y Combinator allows us to use recursion without actually using the recursion that Java already has. And Java 8 actually doesn’t support recursion in lambdas. So this is one way of solving the problem. The simpler one would be to use a recursive Java method and then use a method reference to it (as in MyMathsFunctions::factorial). This is to show that Curry was right and we can do it with nothing but lambda expressions. Since Java is strongly typed I also need an interface, which references itself in the type declaration. This is necessary because at some point we need to apply a function to itself.

There are enough wiki and blog pages and articles on this. Even videos. So I won’t explain it in details. It’s nothing new, just written in Java 8.

	private static <T> T apply(UnaryOperator<UnaryOperator<T>> fn, T arg) {
		return ((Function<UnaryOperator<UnaryOperator<T>>, UnaryOperator<T>>)
				a -> ((Fn2Op<T>) b -> b.apply(b))
				.apply(
					c -> a.apply(
						x -> c.apply(c).apply(x)
					)
				)).apply(fn).apply(arg);
	}

Code on Pastebin

The full Code is here: https://pastebin.com/M2RmRqdU

Encapsulation

In my blog I write about misconceptions. Encapsulation is something you learn when you study Java and OOP. But it seems that most books fail to truly explain the problems you want to solve with it and those you get by using it. Often it’s just a short chapter or even just a small part about the important concepts of OOP. This is leading to misconceptions and poor understanding of OOP.

(Note: I wrote this before the release of Java 10. Expect that some things are somewhat outdated.)

Understanding Java

To be able to use a language you need to actually understand it. This may seem obvious, but books on Java usually don’t have much on understanding the language. When you learn French you will want to be able to translate from and to French. 

What Operations can be performed on a Reference in Java?

In Java it’s important to know what references are and how they are used. So it’s important to know what operations can be performed on references.

Java knows no Constants

Java (both the language and the JVM) are not aware of constants. To reduce confusion it’s better to not use the term “constant” in Java code, unless it’s actually a universal constant.

Dos and Don’ts

Here’s some advice to all who have just begun learning Java. This also serves as an overview to my blog, where I write about all kinds of misconceptions and common problems with programming in Java.

Tuples in Java

Java doesn’t provide tuples. Here are some ideas what you can do about it.

Types of Methods in Java

So in Java there are many kinds of methods. I probably won’t even list half of them but I try to explain how different methods can be.

Functions in Java

There’s a lot of confusion about “functions” in Java. Java doesn’t really have them, but an object could represent a function so it kind of does have them. I try to explain the different meanings of “functions” in Java, other languages and in mathematics.