Question

Is it possible to set a default behaviour for custom (non-native) methods/functions in Java?

For example, I would like to change the default “Function” to do a System.out.println("message") whenever called.

So, when a custom method/function is being created:

public String testMethod()
{
   //custom code
}

it should execute the newly added default behaviour (in this case the system output), before the custom code is run.

Even if this would be a bad excercise, is it possible? Maybe by extending the function class or something?

Answer 1

One way is using Aspect-oriented programming (AOP) for Java: Aspect/J. For what you want, AOP would let you inject code in your program at specific points, e.g. having specified methods execute some println code upon entering or exiting the method. [AOP has a much larger purpose than this simple use for printing debug statements, but I’m trying to stay on target for answering the question.]

This article (possibly somewhat dated) shows an example similar to what you want:

http://www.developer.com/java/other/article.php/3109831/Simplify-your-logging-with-AspectJ.htm