Path: csiph.com!eternal-september.org!feeder.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Cecil Westerhof <Cecil@decebal.nl>
Newsgroups: comp.lang.java.programmer
Subject: Re: Is this the way to work with try with resources
Date: Wed, 09 Aug 2017 06:26:55 +0200
Organization: Decebal Computing
Lines: 82
Message-ID: <87lgmtwels.fsf@munus.decebal.nl>
References: <87poc6wb9n.fsf@munus.decebal.nl>
Mime-Version: 1.0
Content-Type: text/plain
Injection-Info: mx02.eternal-september.org; posting-host="75662a87a83d79e99d1b79ff65a19ab5"; logging-data="8354"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX19XaozSmMq8TJ1/MeNSzUV7uYtC4qwk5Qo="
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)
X-Homepage: http://www.decebal.nl/
Cancel-Lock: sha1:zrEk/F/NGHV3z/Z7zOwC9Ks+NSA= sha1:04nF4s59TuGxB0YRAHvElg4HbzA=
Xref: csiph.com comp.lang.java.programmer:37095

Cecil Westerhof <Cecil@decebal.nl> writes:

> I thought that I could rewrite it to:
>     private static void statistics() {
>         try (Statement stmt     = conn.createStatement();
>              ResultSet rsTotal  = stmt.executeQuery(COUNT_TOTAL_PROV);
>              ResultSet rsUnused = stmt.executeQuery(COUNT_UNUSED_PROV);
>              ResultSet rsUsed   = stmt.executeQuery(COUNT_USED_PROV)) {
>             int    count;
>             String format;
>
>             count  = rsTotal.getInt("no");
>             format = String.format("There are %%,%dd %%6s proverbs.%%n", String.format("%,d", count).length());
>             System.out.printf(format, count, "total");
>             count  = rsUnused.getInt("no");
>             if (count != 0) {
>                 System.out.printf(format, count, "unused");
>             }
>             count  = rsUsed.getInt("no");
>             System.out.printf(format, count, "used");
>         } catch (SQLException e) {
>             System.err.printf("Error in statistics\n");
>             e.printStackTrace();
>             fatalError("");
>         }
>     }
>
> That would be a little better I think, but when there are a lot of
> queries to be done, you need to define a lot of extra result-sets.
>
> But there is a problem with that. If I do that, all three result-sets
> have the same query: the last one.
> What is the reason for this? I am using SQLite3.

I do not know enough about the JDBC. When looking at:
    https://docs.oracle.com/javase/8/docs/api/java/sql/Statement.html

It clearly states that you normally only can have one current
result-set pro statement. It says there:
    All execution methods in the Statement interface implicitly close
    a current ResultSet object of the statement if an open one exists.

But that is clearly not true, because the other ones still work, but
are replaced with the other one.

The solution is to have a statement pro result-set, but than this
statement is only necessary for getting the result-set. So I rewrote
statistics to:
    private static void statistics() {
        try (ResultSet rsTotal  = executeQuery(COUNT_TOTAL_PROV);
             ResultSet rsUnused = executeQuery(COUNT_UNUSED_PROV);
             ResultSet rsUsed   = executeQuery(COUNT_USED_PROV)) {
            int    count;
            String format;

            count  = rsTotal.getInt("no");
            format = String.format("There are %%,%dd %%-6s proverbs.%%n",
                                   String.format("%,d", count).length());
            System.out.printf(format, count, "total");
            count  = rsUnused.getInt("no");
            if (count != 0) {
                System.out.printf(format, count, "unused");
            }
            count  = rsUsed.getInt("no");
            System.out.printf(format, count, "used");
        } catch (SQLException e) {
            System.err.printf("Error in statistics\n");
            e.printStackTrace();
            fatalError("");
        }
    }

And wrote the function executeQuery to make the code a little more
compact:
    private static ResultSet executeQuery(String query) throws SQLException {
        return conn.createStatement().executeQuery(query);
    }

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