...
In this case, the two objects are initially compared using the overriding CalendarSubclass.after() method. This invokes the superclass's Calendar.after() method to perform the remainder of the comparison. But the Calendar.after() method internally calls the compareTo() method, which is delegated to CalendarSubclass.compareTo(). Consequently, CalendarSubclass.after() actually calls CalendarSubclass.compareTo(), and consequently returns false.
Because the The developer of the subclass was unaware of the implementation details of Calendar.after(), she and incorrectly assumed that the superclass's after() method would invoke only its own methods without invoking overriding methods from the subclass. The guideline MET04-J. Ensure that constructors do not call overridable methods describes similar programming errors.
...