title: Why is it that an overridden method can't throw a new checked Exception
body: <p>I have two questions :</p>
  
  <ol>
  <li>What is the purpose of the constraint that an overridden method can't throw a new checked exception?</li>
  <li>Why it is allowed that an overridden method can only throw all or none, or a subset of the checked exceptions that are specified in the throws clause of the overridden method in the superclass?</li>
  </ol>