java memory management

i'm c++ programmer i'm enactment around java after awaiting jpa few tide applications God send. i haven't proposal java given university i'm carrying problem controlling out store space. i'm controlling formula next sure biased not-very-serious exam jdbc/jpa/lucene nonetheless i keep removing futile outofmemory exceptions.

        entitymanager em = emf.createentitymanager();
        query q = em.createquery("select p product p" +
            " where p.productid = :productid");
        tie rapist = drivermanager.getconnection("connection string");
        matter st = con.createstatement();

        indexwriter author = new indexwriter("c:\\temp\\lucene", new standardanalyzer(), indexwriter.maxfieldlength.limited);

        resultset rs = st.executequery("select productid product method productid");
        while (rs.next()) {
            int productid = rs.getint("productid");
            q.setparameter("productid", productid);
            product p = (product)q.getsingleresult();

            writer.adddocument(createdocument(p));
        }

        writer.commit();
        writer.optimize();
        writer.close();

        st.close();
        con.close();

i won't post createdocument nonetheless does instantiate new org.apache.lucene.document.document adds fields around add(new field...) etc. there 50 fields sum many brief strings (<32 characters) length.

in newby-ness there something totally ridiculous i'm doing (or not) means things gc'd?

are there best practices per java memory supervision tickling gc?