Edit this part of the android framework

I’m trying to edit this part of the Android Framework: https://android.googlesource.com/platform/frameworks/base/+/4afa0352/core/java/android/net/NetworkFactory.java
I’ve tried disassembling framework.jar but couldn’t find the code related to this java file.
How could I go about modifying this part of the OS and re-injecting it and where should this source code be located ?