title: abstract class or interface
body: <pre><code>public class C {
    public abstract Boolean methodC();
  }
  
  Class A implements C {
   // all non-abstract methods
  }
  
  Class B extends A {
  // all non-abstract methods
  }
  </code></pre>
  
  <blockquote>
    <p>In Java, can <code>C</code> be an abstract class
    or does it have to be an interface?
    [NOTE: It says - 'A IMPLEMENTS
    C'. Can you IMPLEMENT an abstract
    class in Java?]</p>
  </blockquote>