really
a subclass of java.lang.String. This ensures that the object in question
has no strange, inconsistent, or unpredictable properties.
<p>
To specify that your class is a final class, use the keyword
<code>final</code> in the "modifiers clause" that appears
before the <code>class</code> keyword.
For example, if you wanted to make the ImaginaryNumber class a final
class, its declaration would look like this:
<blockquote>
<pre>
final class ImaginaryNumber extends Number implements Arithmetic {
    . . .
}