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From: Cecil Westerhof <Cecil@decebal.nl>
Newsgroups: comp.lang.java.programmer
Subject: Re: Testing the functionality of sub classes
Date: Sun, 20 Aug 2017 14:49:43 +0200
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Andreas Leitgeb <avl@logic.at> writes:

> Cecil Westerhof <Cecil@decebal.nl> wrote:
>> For example: when creating a new ResultSet through a Statement the
>> previous generated should be closed. With the JDBC driver I use for
>> SQLite3 the old ResultSet is not closed, but becomes a copy from the
>> last generated.
>
> Are you sure about the "copy"? I'd rather expect(*) that the driver 
> re-uses the particular ResultSet instance and returns the same ref
> again.  (*: that is: based on your posted observations. Usually, 
> instance re-use is frowned upon, like premature optimisation, but then
> again, DB driver vendors might have optimised it "well-maturely".)

I am not sure: that is also possible. But what is important is that
the old ResultSet did not get closed. So if I run the test for the
super class with for example MySSQL and this closes the ResultSet (I
do not know, but lets pretend) and I do not also test with SQLite3 I
will not find this bug.


> To verify (or disprove) it, you could run it in e.g. eclipse, and see
> if the same (or a new) "id" appears when you execute another query on
> the same Statement.
>
> Even without a debugger, you could print out the System.identityHashCode 
> for the "two" returned ResultSet references.

Just to satisfy my curiosity I executed (I do not like the formatting,
but that is what Eclipse does):
    try (
            Statement stmt = conn.createStatement();
            ResultSet rsOne = stmt.executeQuery("SELECT 12 AS twelve");
            ResultSet rsTwo = stmt.executeQuery("SELECT 'Hello World!' AS message")
            ) {
        System.out.println(stmt);
        System.out.println(rsOne);
        System.out.println(rsTwo);
    }

And this gives:
    org.sqlite.jdbc4.JDBC4Statement@685f4c2e
    org.sqlite.jdbc4.JDBC4ResultSet@7daf6ecc
    org.sqlite.jdbc4.JDBC4ResultSet@7daf6ecc

So yes, it is like you said: the ResultSet is reused. Is also more
logical. I jumped to a conclusion.

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof