Re: Declaring RuntimeExceptions?

[Stephen Crawley]

Sascha,

> So, should a java compiler accept the following?
> 
> // java.awt.HeadlessException
> //   extends java.lang.UnsupportedOperationException
> //     extends java.lang.RuntimeException
> 
> class Foo
> {
>   void meth() throws java.awt.HeadlessException { }
> }
> 
> class Bar
>   extends Foo
> {
>   void meth() { }
> }

Yes it should.

Refer to the JLS Section 8.4.4.  The last two paragraphs read as follows:

  A method that overrides or hides another method (§8.4.6), including
  methods that implement abstract methods defined in interfaces, may 
  not be declared to throw more checked exceptions than the overridden 
  or hidden method.

  More precisely, suppose that B is a class or interface, and A is a
  superclass or superinterface of B, and a method declaration n in B 
  overrides or hides a method declaration m in A. If n has a throws 
  clause that mentions any checked exception types, then m must have 
  a throws clause, and for every checked exception type listed in the
  throws clause of n, that same exception class or one of its superclasses
  must occur in the throws clause of m; otherwise, a compile-time error 
  occurs.

Note that these rules are for >>checked<< exceptions only; i.e. exception
classes that are NOT subtypes of Error or RuntimeException.

> javac 1.4.1 compiles this code, but gcj 3.2 complains about the throws
> clause (of *Foo*.meth, which is a bit misleading).

gcj 3.2 is clearly wrong, IMO.

-- Steve