What are the steps to customize Class.java of OpenJDK JRE8?

I want to add changes in Class.java file of OpenJDK JRE 8(for example I want to add a simple System.out.println() statement). I want to compile this file and patch it in jar(rt.jar). What are the jars should be part of this class path and is there any predefined steps for this.

http://hg.openjdk.java.net/jdk8/jdk8/jdk/file/687fd7c7986d/src/share/classes/java/lang/Class.java

Thanks