There should be no reason why you would need Java class files. The Java source code exists and allows you to read, edit, and recompile the explorer. The GWT compiler will then emit the compiled JavaScript output.
For what purpose do you need the class file? If you do definitely need it, consider using javac to compile the provided source down to bytecode.
WesleyMoy, thanks for the clarification. Yes, Explorer.class is no use at all after the GWT compilation, neither is Examples.class. I thought those EntryPoint classes might be needed at run-time since Examples.class is included in the WAR file.