Compare inheritance and composition, the two fundamental ways to relate Java classes, then practice debugging ClassCastExceptions in Java inheritance.

For example, a Java program obtains file I/O (input/output) services by creating objects from various file-related classes in Java’s class library and calling their methods.

A method might accept a specific type and its subclasses, but you want to restrict usage to a select few implementations of your own design. Java's open inheritance model can feel like an open ...