Effective Java, Third Edition

Default methods are, however, extremely useful for providing standard method implementations when an interface is created, to ease the task of implementing the interface (Item 20).

eliminate the class’s self-use of overridable methods entirely. In doing so, you’ll create a class that is reasonably safe to subclass. Overriding a method will never affect the behavior of any other method.

The toString method should return a concise, useful description of the object