Using keyword abstract in methods in java
<p>As per <a href="http://books.google.co.in/books?id=6vwJlH1aYCUC&amp;printsec=frontcover&amp;dq=the+java+programming+language&amp;hl=en&amp;ei=Vj4zTdPZKsPXrQeokJ3lCA&amp;sa=X&amp;oi=book_result&amp;ct=result&amp;resnum=1&amp;ved=0CDMQ6AEwAA#v=onepage&amp;q&amp;f=false" rel="nofollow">The Java Programming Language(by Arnold Gosling)</a> (ref pg. 275) if we use <code>abstract</code> explicitly before a method declaration in an interface, We can</p>

<blockquote>
  <p>skip the method method in the implementation class.</p>
</blockquote>

<p>As per the example:</p>

<pre><code>interface Sheet{
  public double computeArea();
  public abstract double computePerimter();
} 

class Sphere implements Sheet{
  // Some data members and constructors.

public double computeArea() { ... }

  // No implementation of computePerimeter  
}
</code></pre>

<p>But when i tried creating an object of the Sphere class, i showed up an error that the computePermeter method hasnt been overloaded(that should has been the case).</p>

<p>But as per the context, you could <code>skip</code> the method if it has been <code>explicitly declared</code> as <code>abstract</code>.However there has to be a class implementating that method. Arent the methods in an interface implicitly abstract?? Or am i interpreting it wrongly?? The <code>explicit abstract</code> has confused me a bit.. please help.. <img src="http://i.stack.imgur.com/8z4LL.png" alt="alt text"></p>

<p><img src="http://i.stack.imgur.com/Ngsa7.png" alt="alt text"></p>

<p><img src="http://i.stack.imgur.com/6aiUg.png" alt="alt text"></p>
