rent package.
By default classes can only be used within the package in which they
are declared.
<p>
For example, the ImaginaryNumber class should be declared public because
we want other classes and objects to have access to this class. Thus
the class declaration for the ImaginaryNumber class now looks like this:
<blockquote>
<pre>
public final class ImaginaryNumber extends Number implements Arithmetic {
    . . .
}
</pre>
</blockquote>
By convention, when you use the <code>public</code> keyword in a class