title: toString in subClasses Cannot Override abstract toString , Java
body: <p>I have this very long exercise and I came a cross a problem in each sub class.
  The problem says  and I have no idea what mistake I've made while writing.
  If you could check the 4 toString methods I would be much apprecaited .</p>
  
  <p>The code is here: <a href="http://paste.org/pastebin/view/39488" rel="nofollow noreferrer">http://paste.org/pastebin/view/39488</a> 
  I know I should past the code here but it is very long and I'm not able to organize it well.</p>
  
  <p><code>toString() in Shape cannot override toString() in java.lang.Object; attempting to use incompatible return type</code></p>
  
  <p><code>toString() in Square cannot override toString() in java.lang.Object; attempting to use incompatible return type</code>
  `</p>
  
  <p><code>toString() in Sphere cannot override toString() in java.lang.Object; attempting to use incompatible return type</code></p>
  
  <p><code>toString() in Cube cannot override toString() in java.lang.Object; attempting to use incompatible return type</code></p>
  
  <p>thanks</p>