title: Dart any differences between with or without abstract keyword?
body: <p>Hi I just would like to know if there is any difference between giving abstract keyword or not like so.</p>
  
  <pre><code>// with
  abstract class A {}
  
  class B extends A {}
  
  // without
  class A {}
  
  class B extends A {}
  </code></pre>
  
  <p>Should I give it?</p>