Re: non-static method gotcha

From:

Lew <noone@lewscanon.com>

Newsgroups:

comp.lang.java.help

Date:

Sun, 15 Mar 2009 21:03:23 -0400

Message-ID:

<gpk8gs$rr8$1@news.albasani.net>

Roedy Green wrote:

I was getting an compiler error message: non-static method cannot be
referenced from a static context. I am quite familiar with the
message, and normally I know what the problem is. This time I was
hitting a brick wall trying to figure it out. See if you can see the
problem. Hint, enum possibilities are their own little classes.

enum SubmissionSite
    {
        ABABASOFT( "AbabaSoft",
"http://www.ababasoft.com/catalog/submit.php" )
                {
                /**
                 * Simulate manual submit
                 *
                 * @param pad URL of the pad xml file we are
submitting.
                 */
                String submit( String pad )
                    {
> > > > > > > > > > return submitViaPost( "/checkadd.php",
                            "padurl", pad,
                            "psubmit", "Submit PAD File"
                    );
                    }
                }, // end ABASOFT

.......

/**
     * submit pad via POST with given parms
     *
     * @param action action, usually with lead /
     * @param postParms parm=value pairs, including parmurl=pad
     *
     * @return text the website sent back.
     */
    private String submitViaPost( String action, String... postParms )
        {
...
        }

    /**
     * Submit the PAD to this submission site.
     *
     * @param pad URL of pad e.g. http://mindprod/pad/fileio.xml
     *
     * @return what site said back, raw.
     */
    abstract String submit( String pad );

} // end SubmissionSite

The reason is that enums with bodies are implemented as nested subclasses of
the declared enum, 'SubmissionSite' in your example. The error message spoke
of non-static method in a static context because the only way for a nested
class to access a private method of the outer class is via an outer reference,
in this case a non-static one. The subclass cannot inherit a private method,
and being an enum is a static nested class, hence the error.

When you have a package-private or wider scope for the method in the outer
class, the nested subclass inherits it, so the question of static context goes
away.

--
Lew