Aria sketched a class in her notebook: name, health, energy, and a sing method. She made sing protected so derived species could override it. Next she created Bird and Beetle subclasses. Bird added a wingSpan property and overrode sing to produce a melody; Beetle implemented a hardShell boolean and sang a single click.
Basic concepts (objects, classes, data abstraction, encapsulation, inheritance, polymorphism). programming with java 4th edition balagurusamy ppt