[2042] in java-interest
throws declataration in Java/beta
daemon@ATHENA.MIT.EDU (Ken Arnold - Sun Labs)
Fri Sep 22 08:05:59 1995
Date: Thu, 21 Sep 1995 11:26:56 -0400
From: arnold@cocolat.East.Sun.COM (Ken Arnold - Sun Labs)
To: pambrose@weblogic.com
Cc: java-interest@java.Eng.Sun.COM
>Paul Ambrose sez:
>
>In beta Java, if object A extends object B, and both implement method
>foo(), A.foo() *cannot* throw exception X unless B.foo() also
>throws X. If you declare that A.foo() throws X, the compiler
>will complain that B doesn't also throw X.
To be more precise, A.foo() cannot thrown an exception that is not in
B.foo()'s throws clause. A.foo() can have its own throws clause that
is different from B.foo()'s as long as all elements of A.foo() would be
throwable by B.foo(). For instance, if B.foo() throws Gogin, then
A.foo() can be declared to throw either Gogin or any extended class of
Gogin.
>This means that you can NEVER throw an exception from a
>toString() method because Object.toString() doesn't throw
>any exceptions.
>
>Is this correct?
Yes. Anything else would be a violation of the contract. Analagously,
you cannot say that A.foo() returns an int if B.foo() returned a
short.
Ken Arnold
-
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