Drawable and Cloneable. Also the interface Drawable is a part of the package algebra . Both algebra.sentence and algebra.table are composed of algebra. As you can see, there are seven kinds of Words . All subclasses of algebra.
Words implement the algebra.
Drawable interface and hence can draw themselves. Once the user enters a value in the text field, it is read using Integer.parseInt. Exceptions, if there are any, are handled and the value is passed to the relevant method in the application applet. Inside the method calculations are performed and entity s are built one at a time. That is, an answer is built line by line.