An applet is a small embeddable Java program. In our course, we will set up HTML files that will run our applets. What you will write are subclasses of the Applet class. The Applet class is a subclass of Panel which in turn is a subclass of Container , which in turn is a subclass of Component , which in turn is a subclass of the Object class. Component implements an interface named ImageObserver .
Interfaces provide specification for behavior that are adopted and implemented by classes.
Knowing the class hierarchy in an object oriented framework is not always necessary, but at times useful. When considering the big picture, as discussed earlier, learning to become a class user is as important as learning to develop algorithms. Traversing Java API for the right class or method is an important part of programming with Java and it is best that you get used to it now. For the most part, when developing applets, you will have examples to guide you on what methods to write. The functionality provided for applets is not fully specified at that level, much of it is defined in the classes leading to it.