How do I calculate the difference between two calendar dates in Java?

It must be done manually without using date or calendar methods. Or where can I obtain the source code that forms those methods?

How do I calculate the difference between two calendar dates in Java?
You don't need the source code (since you can't modify the variables in the object so it won't do you much good). All you need is the interface which is available on the sun website. I've linked to it in the sources. Good luck.