How to remove System.out.println's from codebase

Question

We have a huge (old legacy java) code-base, where many files (around 5k) have System.out.println\'s. We are planning to remove them for cleanup/performance reasons. How can

Answer 1

You could use a conditional compilation to have a debug build with the print statements and a release build without them.

Basically, the idea is to create a final static class with a final static boolean that you use as a switch at compile time.

public final class Debug {
   //set to false to allow compiler to identify and eliminate
   //unreachable code
   public static final boolean ON = true;
}

Then you can just replace all of your System.out.println statements with

if(Debug.ON)
{
    System.out.println...
}

Since the compiler will ignore any unreachable branches of code, you can just set ON = false when you do a release build and the print statements will be excluded from your bytecode.

Note: This doesn't deal with the case that Oscar pointed out, where a print statement may change the state of some object. You could use conditional compilation to print to a null object when in release mode, as he suggested, instead of removing the prints altogether.

Answer 2

Have you considered editing those source files to remove the lines?

You might find that it will only a developer a couple of days to go through and get rid of most of them. We had a similar issue and I just got up really early and went through all our files getting rid of rubbish.

I used Eclipse and the clean up on save feature to cleanup imports and stuff at the same time.

Its quite a therapeutic thing to do!