Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException

[nikx_8_7]

i am making an application for a online test.... i hav stored question and ans in sql server 2005.
But when i compare the correct ans with ans supplied by users i get following


Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at online1.actionPerformed(online1.java:685)
at javax.swing.AbstractButton.fireActionPerformed(Unk nown Source)
at javax.swing.AbstractButton$Handler.actionPerformed (Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed (Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseRe leased(Unknown Sour
ce)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent( Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(U nknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unkno wn Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilter s(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(U nknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarch y(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)




Plz Help

[Steve11235]

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at online1.actionPerformed(online1.java:685)

The top line of the stack trace tells you everything except the name of the field that is null. Look at your code...

[nikx_8_7]

:confused:
i don't understand what you are saying ... can u plz elaborate???

[dswastik]

You get a NullPointerException, when you call a method on any reference variable which is not initialized, means its holding a null reference.

For e.g.

public class MyClass{
  String s;
  public static void main(String arg[]){
       MyClass mc=new MyClass();
       System.out.println(s.length());  // will throw a nullpointerexception as variable s has not been initialized.
  }
}

So look at your code properly and make sure that you are not committing any such mistake.

[dswastik]

Sorry there was a small mistake in the code

System.out.println(s.length());

should be

System.out.println(mc.s.length());

[nikx_8_7]

i get this exception when i try to compare 2 arrays which hold the records retrieved from sql server 2005....here's the code snippet...

try
{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Connection con=DriverManager.getConnection("jdbc:odbc:A1","", "");
st=con.createStatement();
res=st.executeQuery("select * from store");

while(res.next())
{
userans[i]=res.getString(1).trim();

System.out.println(userans[i]);
i++;
}

}
catch(Exception fggf)
{
System.out.println("exception occurred2"+fggf);
}
l20.setText(String.valueOf(count1));

//-------------------------gett---------------------------

try
{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Connection con=DriverManager.getConnection("jdbc:odbc:A1","", "");
st=con.createStatement();
res=st.executeQuery("select * from ans");

while(res.next())
{
getans[j]=res.getString(1).trim();
System.out.println(getans[j]);
j++;

}
}
catch(Exception erb)
{
System.out.println(erb+" while getting original answers ");
}

for(int z=0;z<5;z++)
{
if(userans[z]==getans[z])
counter++;
}


counter counts number of correct ans

[vkorenev]

at online1.actionPerformed(online1.java:685)

This means that you should look at line 685 in online1.java.