Changing the code of the class from jar file

Question

How can I read (load) the java class from jar file, add some code to the class and then put back to the jar? I need to write a script (a java code) which does all these thin

Answer 1

A jar is just a ZIP file, so you can extract it with any archive manager like 7-ZIP. It will contain class files, which are compiled Java files. You need a Java decompiler to read and modify the bytecode.