explicitly, put the keyword <code>extends</code>
followed by the superclass name directly after the name of the class that
you are declaring. So this class declaration
<blockquote>
<pre>
class ImaginaryNumber extends Number {
    . . .
}
</pre>
</blockquote>
explicitly declares that the Number class is the superclass of the
<code>ImaginaryNumber</code> class. (The Number class is part of the java.lang
package and is the base class for Integers, Floats and other numbers.)
</blockquote>

<h4>Interfaces</h4>
<