This class defines no slots of its own but will inherit slots from both of its direct superclasses, including the slots they inherit from their superclasses. That is, if classes could have only a single direct superclass, ordering classes by specificity would be trivial--a class and all its superclasses could be ordered in a straight line starting from the class itself, followed by its single direct superclass, followed by its direct superclass, all the way up to T. But when a class has multiple direct superclasses, those superclasses are typically not related to each other--indeed, if one was a subclass of another, you wouldn't need to subclass both directly. Not all coin machines are created equal. A tool like VisualVM or YourKit connects directly to the Java Virtual Machine and takes a series of snapshots of what methods are actually run by the CPU at specific point of time and then calculates the stats.