If I guessed right, you have written a software which wants to change itself from a trial version to a licensed version, by copying the appropriate class files or java files. The concept itself is way out.... and your question does not reflect your need correctly if so. Software license enabling does not work this way.
If you think about it, and read about the concepts of class loading, program execution fundamentals and a few more topics, you would find a better way of approaching your problem.
You should rethink your strategy for this.