Does this mean anything? Decifering Exceptions

[mallorz]

I am struggling with my current Java assignment and can't figure out how to use the debugger to step though a GUI application to see what exactly is happening where.

When I populate all fields in my GUI and they are validated successfully, the end message does not appear. Instead, in the console window, I get the following exception pointing to my printInvoice() method indicating a NullPointerException.

As I said, everything has been filled out correctly and this program at least mostly-operated yesterday morning. Is there a way to find out where this is coming from using the message below? I suspect it is stemming from the date fields I added and will look into that but I am still curious. I would guess not but maybe someone out there can offer me some advice and/or tell me how (if) the debugger tool can be used.

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at edu.witc.Ch_08_10ex2.controller.Hotel_Processor.printInvoice(Hotel_Processor.java:219)
	at edu.witc.Ch_08_10ex2.controller.Hotel_Processor$SubmitButtonListener.actionPerformed(Hotel_Processor.java:61)
	at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
	at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
	at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
	at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
	at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
	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(Unknown Source)
	at java.awt.LightweightDispatcher.dispatchEvent(Unknown 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.dispatchEventImpl(Unknown Source)
	at java.awt.EventQueue.access$200(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
	at java.awt.EventQueue$4.run(Unknown Source)
	at java.awt.EventQueue$4.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
	at java.awt.EventQueue.dispatchEvent(Unknown Source)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.run(Unknown Source)

P.S. Yup! It's from the date - just commented out the fields. But seriously, this debugger thing?

[gimbal2]

to be honest, I find using a debugger to debug a Swing application pretty hairy because it involves multithreading. I'd try to find problems by sprinkling System.out statements first if I were you.

[SurfMan]

One other thing you can do, that is *if* you use a decent IDE like JetBrains IntelliJ IDEA, is to set Exception breakpoints. In IDEA you can set a breakpoint to stop your program on certain conditions, like the occurance of a NPE, AIOOBE and what have you.

[Norm]

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at edu.witc.Ch_08_10ex2.controller.Hotel_Processor.pr intInvoice(Hotel_Processor.java:219)

There is a variable with a null value on line 219. Look at line 219 in the your source and see what variable is null. Then backtrack in the code to see why that variable does not have a valid value.
If you can not tell which variable it is, add a println just before line 219 and print out the values of all the variables on that line.

[mallorz]

I managed to get the debugger to work. The issue seems to lie in my customer class - everything was null. I was messing around yesterday and I guess I forgot to change a few things back there. Thanks guys.

I believe that ultimately leaves me with one more issue to overcome and then I can have this thing over with! :)

[gimbal2]

One other thing you can do, that is *if* you use a decent IDE like JetBrains IntelliJ IDEA, is to set Exception breakpoints. In IDEA you can set a breakpoint to stop your program on certain conditions, like the occurance of a NPE, AIOOBE and what have you.

Hm, that's very interesting. Although you can basically do that in any IDE by setting a breakpoint in a specific method of the Exception you want to trap. I've seen a colleague do that without even having the source code.