Please don’t add a new question to an existing discussion. I have separated your question off.
Not sure. But I think the .class files are all bundled into a file called rt.jar. So explore your Java™ installation folder and find rt.jar. On a Linux box, you can use Archive Manager to explore the contents of that file, but I don’t know whether there is a corresponding program on Windows®. If you can’t explore it, try copying it to a temporary location and unzipping it. Then you can explore it and play with it, secure in the knowledge you aren’t damaging your installation because you took a copy.