Javassist (Java programming assistant) makes bytecode engineering simple. It is a class library for editing bytecode in Java; it enables Java programs to define a new class at runtime and to modify a given class file when the JVM loads it.

The most significant class of this package is CtClass. See the description of this class first.

To know the version number of this package, type the following command:

java -jar javassist.jar

It prints the version number on the console.