java - exporting data into double array -
i want add retrieved data database array, retrieval data null. mistake? please me.
for (user u : userlists) { (resource r : resourcelists) { string ratingquery = "select rank ratings userindex='" + u.getindex() + "' , resourceindex='" + r.getindex() + "'"; try { ratingcon = connectionmanager.getconnection(); stmt = ratingcon.preparestatement(ratingquery); rs = stmt.executequery(); while (rs.next()) { rate = rs.getdouble("rank"); ratings[u.getindex()][r.getindex()] = rate; //it seems here problem } } catch (exception e) { system.out.println("log in failed: exception has occurred! " + e); } } }
there no problem in line, if ratings
2-dimensional array of double:
ratings[u.getindex()][r.getindex()] = rate;
but may database returns empty resultset
? insert print statement debug:
while (rs.next()) { rate = rs.getdouble("rank"); system.out.println("result set not empty! current rank is: " + rate); ratings[u.getindex()][r.getindex()] = rate; //it seems here problem }
if prints nothing - problem not in code in db data. think missed semicolon ;
@ end of query.
and exception handling:
catch (exception e) { system.out.println("log in failed: exception has occurred! " + e); }
the exception type catch here abstract - can't know whether sqlexception
exception or arrayindexoutofboundsexception
. change several catch blocks.
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