title: Compile-time error or runtime error
body: <p>for example <code>Class B extends A</code>.
  An object <code>A test= new B (x,y)</code>;
  Then a method that there is only on Class <code>B</code> is invoked on the <code>test</code> object.
  Will it be a Compile time error or a run time error?
  Overall what are the different between both errors.</p>