Re: Why does Java require the throws clause? Good or bad language design?

From:

Lew <lew@nospam.lewscanon.com>

Newsgroups:

comp.lang.misc,comp.lang.java.help,comp.lang.java.programmer

Date:

Mon, 19 Feb 2007 20:38:03 -0500

Message-ID:

<EOSdnYyKB8VhzUfYnZ2dnUVZ_smonZ2d@comcast.com>

Michael Rauscher wrote:

or if you a checked exception should be thrown,
declare it in CBF#execute's throws-clause.

Arthur J. O'Dwyer wrote:

That would be nice, but you just said that Java won't allow you to
do that. ("This would lead to a compile-time error ...")

That is not what he said. In fact, he said the exact opposite.

He said the error would come from NOT declaring the checked exception in the
signature. That error would be fixed if CBF and its implementors declared the
exception for the method.

CBF callBankFunc = new CBF() {
    public void execute( int x ) {
        if ( x == 42 )
            throw new Exception();
    }
};

This is what Michael said would cause a compiler error if execute() did not
declare the Exception in its signature.

interface CBF {
public void execute(int x) throws Exception;
}

This is what Michael said would allow the implementing class to throw that
checked Exception, because now it is part of the signature. (The implementing
class would also need to include the throws clause in its signature in order
to throw the checked Exception, because it is part of the signature just like
the int argument is.)

- Lew