title: Giving the parameter System.out::println to a method
body: <p>I forgot a concept that I used and can't remember it.</p>
  
  <p>For the context, I used to have a method like <code>toString()</code> which had a parameter. This parameters allowed me to call my method like <code>myMethod(System.out::println)</code> to print it on the screen, but also to print it in a file with the same syntax.</p>
  
  <p>Does anyone know what can be this parameter? the concept?
  I think it's kind of a <em>FunctionalInterface</em> but I don't know what it is.</p>