What the ****? Operator Overloading in Java

Daniel Winterstein

@winterstein

CTO at SoDash

C++

Algol

MyVec MyVec::operator+(MyVec vec)
        { /* code */ }

Examples of Madness

Custom Operators from Scala Graph project:

1 ~ 2 % 5 Creates an edge with weight 5
~%#+ Create key-weighted labeled undirected edge

~%+# Create weighted key-labeled undirected edge

Make Array + Array mean bitwise xor of the elements via implicit conversion

implicit class ByteArrayOps(private val a1: Array[Byte]) extends AnyVal {
  def + (a2: Array[Byte]): Array[Byte] =
    (a1 zip a2).map { case (x, y) => (x^y).toByte }
}

James Gosling →

Java →

Old school

vestments →

So How Do We Do It?

You can alter the compiler:
- Javac 7 has annotation processors
- Javac 8 has plugins
& Artem Melentyev has: https://github.com/amelentev/java-oo
With plugins for Eclipse, IntelliJ, and NetBeans

Why is overloading great?

Concise
Clear: Let the maths shine through

Why is overloading dubious?

- Changes the language.

- Precedence: no right solution for parsing.

E.g. We know how to parse

a + b * c

but how should we parse

a ¬ b " c

- But Java-OO is limited: no custom operators