Question

So I have an application that I start on 2PC. Each instance launches an HSQLDB in server mode.

I’m trying to get the sales of different products.

So I query the local database and fill an arraylist with the name of the product and the number of sales.

Then I execute the same query on the other database on the other PC.

For 1 product, I so have two lines (each one correspond to one database).
Here, results are false but the execution time is ok.

In order to manage that, I did the following :

ResultSet rs2 = state2.executeQuery(produitsQuery);
while (rs2.next()) {
   for (int i = 0; i < produits.size(); i++) {
       obj = ((Object[]) produits.get(i));
       idpdt = (Integer) obj[1];

       if (idpdt == rs2.getInt(1)) {
           nb = (Integer) obj[3];
           valo = (Double) obj[4];

           nb += rs2.getDouble(4);
           valo += rs2.getDouble(5);
           produits.set(i, new Object[]{
               rs2.getString("famille"),
               rs2.getInt("id_pdt"),
               rs2.getString("nom_pdt"),
               nb,
               valo,
               s2.getString("sous_famille")});
           k = 1;
       }
    }
    if (k == 0) 
        produits.add(new Object[]{
            rs2.getString("famille"),
            rs2.getInt("id_pdt"),
            rs2.getString("nom_pdt"),
            rs2.getInt("nb"),
            rs2.getDouble("valo"),
            rs2.getString("sous_famille")});

}

Results are perfect but the execution time is very very slow and that’s a problem. I think it’s because I loop the entire arraylist at every row of the resultset.

What others solutions might I use to make the execution time faster?

Answer 1

Why not put your first result set into a HashMap, keyed on idpdt (since that’s what you’re indexing by) ? A HashMap will provide O(1) lookups, rather than O(n).

Your code would look like:

while (r2.next()) {
   Object[] result = map.get(rs2.getInt(1));
   if (result != null) {
      ...
   }
}