In packages you can define a Debug - Level. It has four modes:
Mode "0: Disabled" means that no debugging information is shown.
Mode "1: DEBUG=false" means that all classes of the package get a final Bool - Variable being initialized with "false".
Mode "2: DEBUG=true" means that all classes of the package get a final Bool - Variable being initialized with "true". Now you can show debugging information in all classes using the codelines "if (DEBUG)...". If you don't need them anymore, simply reset to mode 1.
Mode "3: Method-Tracing" prints - as soon as any method of a class is called - the arguments of the called method to System.out. This mode causes much output, so you should use it only in special cases.