Re: Statements before super()

From:

"Mike Schilling" <mscottschilling@hotmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 9 Feb 2010 10:53:33 -0800

Message-ID:

<hksave$lt1$1@news.eternal-september.org>

Lew wrote:

Eric Sosman wrote:

[...] If it were possible to
run arbitrary code on a Sub instance before its Super-ness had
been established and its Super invariants put in place, you'd
be working with a Sub that was a Super in name only, but not in
actuality.

Steven Simpson wrote:

Could that restriction not be loosened in a compiler-verifiable way,
i.e. check that no statement prior to super() uses 'this'
(explicitly or implicitly)? Therefore, there would be no arbitrary
code acting on the Sub instance, until after super().

Mike Schilling wrote:

You can accomplish this in a roundabout way by calling a static
method in the arguments to "super()"

The method doesn't have to be static.

It does:

import java.io.*;

class Test extends FilterInputStream
{
    Test() throws Exception
    {
        super(getStream());
    }

    InputStream getStream() throws Exception
    {
        return new FileInputStream("foo.txt");
    }
}

% javac -g Test.java
Test.java:7: cannot reference this before supertype constructor has been
called
        super(getStream());
              ^
1 error