How to change and replace class file?

Question

Java

Good afternoon! I have jar' nick. With the help of debugging, I found in which class the NPE error occurred. How can you change this compiled class through the idea, build it and replace it in the original jar?

Answer 1

Jar is like a zip.
you change the extension to zip, unpack, replace the class (if there were no changes in the signatures of public methods), pack it back, change the extension back from zip to jar