What is the groovy << operator mean in this context?

Question

In a groovy tutorial, I encountered the following code:

class DateTagLib {
  def thisYear = {
    out << Calendar.getInstance().get(Calendar.YEAR)
  }
}

I don't know what the << means, and I'm having no luck with google.

Edit: I now know that << sometimes is a bit shift. But what does it mean here?

Answer 1

It's used for bit-shift operations. More info:

http://groovy.codehaus.org/Bitwise+Operations

Answer 2

In groovy, the bitwise operators can be overridden with the leftShift (<<) and rightShift (>>) methods defined on the class. it's idiomatic groovy to use the leftShift method for append actions on strings, buffers, streams, arrays, etc and thats what you're seeing here.

http://groovy.codehaus.org/groovy-jdk/java/io/OutputStream.html

Youre looking at a grails tag lib, so out represents the page that's being rendered. The results off this taglib will be added to the output buffer that will be rendered to the client.