Why can't overriding methods throw exceptions broader than the overridden method?

Question

I was going through SCJP 6 book by Kathe sierra and came across this explanations of throwing exceptions in overridden method. I quite didn\'t get it. Can any one explain it

Answer 1

Well java.lang.Exception extends java.lang.Throwable. java.io.FileNotFoundException extends java.lang.Exception. So if a method throws java.io.FileNotFoundException then in the override method you cannot throw anything higher up the hierarchy than FileNotFoundException e.g. you can't throw java.lang.Exception. You could throw a subclass of FileNotFoundException though. However you would be forced to handle the FileNotFoundException in the overriden method. Knock up some code and give it a try!

The rules are there so you don't lose the original throws declaration by widening the specificity, as the polymorphism means you can invoke the overriden method on the superclass.