Factual questions about java
<p>My teacher gave out a practice exam on java recently and I'm curious to see how I did on the true/false part.  I'm least confident about number one, so any explanation there would help a lot.  </p>

<ol>
<li><p>In Java, a class can extend any number of abstract classes.<br/></p>

<blockquote>
  <p>false.  I don't quite understand why, is it just because in an inheriting class the the parent classes could cause a conflict?</p>
</blockquote></li>
<li><p>In Java, it is illegal to pass a parameter whose type is an abstract class.<br/></p>

<blockquote>
  <p>False, abstract classes don't even have constructors...</p>
</blockquote></li>
<li><p>In Java, an abstract class can have any number of subclasses.<br/></p>

<blockquote>
  <p>True.  I can't think of anything that would restrict this.</p>
</blockquote></li>
<li><p>In Java, there is no restriction on the number of interfaces a class can implement.<br/></p>

<blockquote>
  <p>True </p>
</blockquote></li>
<li><p>It is not possible to implement a stack as a doubly-linked list, because a stack requires access to only one end of the list, and a doubly-linked list provides access to both ends of the list.</p>

<blockquote>
  <p>true.  but it wouldn't be very efficient.</p>
</blockquote></li>
</ol>
