libjavassist-java - 1:3.23.1-1 main

This library makes Java bytecode manipulation simple. It enables Java
programs to define a new class at runtime and to modify a class file
when the JVM loads it.
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Unlike other bytecode editors, Javassist provides two levels of API:
source level and bytecode level. With the source-level API, users can
edit a class file without knowledge of the specifications of the Java
bytecode. You can even specify inserted bytecode in the form of source
text; Javassist compiles it on the fly. On the other hand, the
bytecode-level API allows the users to directly edit a class file as
other editors.