What does the arrow operator, '->', do in Java?
That's part of the syntax of the new lambda expressions, to be introduced in Java 8. There are a couple of online tutorials to get the hang of it, here's a link to one. Basically, the -> separates the parameters (left-side) from the implementation (right side).
The general syntax for using lambda expressions is
(Parameters) -> { Body } where the -> separates parameters and lambda expression body.
The parameters are enclosed in parentheses which is the same way as for methods and the lambda expression body is a block of code enclosed in braces.
This one is useful as well when you want to implement a functional interface
Runnable r = ()-> System.out.print("Run method");is equivalent to
Runnable r = new Runnable() { @Override public void run() { System.out.print("Run method"); }};
I believe, this arrow exists because of your IDE. IntelliJ IDEA does such thing with some code. This is called code folding. You can click at the arrow to expand it.