Debugging using Java source code

Question

Is there a way to include whole Java source code into an eclipse project so the program is easier to debbug (e.g. by inserting println in methods you otherwise couldn't insert anything)?

I have a bug in my code. But to better understand why the bug in my code appears, I'd like to see what intermediate results in some system method (on which use the bug occurs) are.

For example, I'd like to know what JViewPort.scrollRectToVisible() exactly does and how my input behaves in it by printing out some intermediate results that occur in the method itself.

EDIT:

Instead of using JRE System Library X, I want to add the source code from JDK as if I had written the code myself. I want to be able to edit any System class just as I am able to edit any class I created myself. I want editable .java files, not packed .jars...

Answer 1

You cannot change the library code, but you can view it by using de-compiler. The max you can do is this. Now if you change any code in the libraries which you reached via the de-compiler, you would find an error stating "the integrity of the .jar package has changed which is not allowed"

Answer 2

Eclipse have built-in support for what you wanna do.

All you have to do is set breakpoint and execute application in debugging mode.

You can use these icons in Eclipse debugging perspective.

Follow along Eclipse Debugging Tutorial for details.

Answer 3

You would need to add the 3rd-party library to your Eclipse workspace as an project. (How you would do that depends on the code you are dealing with.) Once you have done that, you can hack your copy of the library to add trace prints etcetera.

A better alternative is to simply attach the source code for the 3rd-party library so that the debugger can show you source as you step through the code, set breakpoints,. Then use "advanced breakpoint" techniques instead of trace prints; e.g. http://www.vogella.com/articles/EclipseDebugging/article.html#advanced