Java™ How To Program (Early Objects), Tenth Edition

Using a Nested Class to Implement an Event Handler

All the classes discussed so far were so-called top-level classes—that is, they were not declared inside another class. Java allows you to declare classes inside other classes—these are called nested classes. Nested classes can be static or non-static. Non-static nested classes are called inner classes and are frequently used to implement event handlers.

An inner-class object must be created by an object of the top-level class that contains the inner class. Each inner-class object implicitly has a reference to an object of its top-level class. The inner-class object is allowed to use this implicit reference to directly access all the variables and methods of the top-level class. A nested class ...