NullPointerException at com.mysql.jdbc.Statement.executeQuery

Question

hi,
i use mysql, mm-mysql driver. In code, 4 different types of queries are present i use 4 kind of threads that retrive data from database (for each type of query) every 5 secs.Code sometimes works and sometimes throws null pointer exception.Although i used different result sets for each type of query, problem still remains. what can i do? what is the exact source of problem?
thanx in advance
hELin

Answer 1

GuiSample.java :
public class ThreadIncoming implements Runnable
private boolean suspend; // Flag indicating that we should suspend the loop
private Thread thread;
public ThreadIncoming()
start();
public void start()
thread = new Thread(this);
suspend = false;
thread.start();
public void suspend()
// Set the suspend flag - when the run loop comes back round it will check this and wait
suspend = true;
public synchronized void resume()
// Unset the suspend flag - the call to notify will wake up the waiting Thread which will then continue
suspend = false;
notify();
public void stop()
thread = null;
resume(); // Call resume in case stop is called while waiting
public void run()
if (queryApp != null && queryApp.isConnected() ) {
while(Thread.currentThread() == thread) {
if (filterIncomingRuns)
suspend();
if(suspend) {
// Check whether the suspend flag is set - get the current Thread to wait if it is
synchronized(this)
while(suspend) {
try {
wait();
catch (Exception e1) {
e1.printStackTrace();
try
fillAlarmTable();
Thread.sleep(5000);
catch(InterruptedException e)
private void fillAlarmTable() {
queryApp.getTable(logAlarmTable);
...//END OF GuiSample.java
In this class, the thread type used is above shown. Every thread's task is to retrive data from DB and insert it into jtable's in GuiSample.java...
QueryDB.java: where DB operation are done
getTable(jtable theTable) {
stmt = connection.createStatement();
if (theTable.getModel().getClass().getName().equals("LogAlarmTableModel")) {
rsAlarm = stmt.executeQuery(sql);
displayRS(rsAlarm,theTable);
else if ....
stmt.close();
i tried to write some part of the code..waiting for ur advice. thanx
hELin