Throws Exception catch childException... why not? : Say I have a method doSomething() which throws a checked exception, then in my main method I enclose doSomething() in a try catch.

Question:
Say I "throws Exception" in doSomething(). Why can't I "catch (ChildException e)" in my main method?

I know I can't and that I must catch Exception, but I don't understand why.

ChildException extends Exception.

If I throws ChildException and catch Exception then there's no problem understandably so. Why not the other way round?