Exception in event handler error - is it scope?

Programming Questions

hondaman9..

Exception in event handler error - is it scope?

in Programming Questions • 1 year ago

I declare two global integer arrays BoxX[] and BoxY[] at the beginning of my program.

int BoxX[];
int BoxY[];

I have a procedure void loadTemplateData(int Tnum) - code below - to read a text file and stuff the arrays with integers from the text file. I can read and parse the numbers and display them back no problem, but as soon as I try to put the values into array slots I get the following error:

############# EXCEPTION IN EVENT HANDLER #############

An error occured during execution of the eventhandler:

CLASS: JupiterShowDemo_v6_G4P_b METHOD: handleButtonEvents

Caused by java.lang.NullPointerException

JupiterShowDemo_v6_G4P_b.loadTemplateData(JupiterShowDemo_v6_G4P_b.java:608)

########################################################

When I comment out the lines that fill the array the procedure runs fine and displays the results in println statements. As soon as I un-comment the array fillers it runs the last println statement before filling the array and then throws the error.

I know the error refers to the G4P library but I think this is a programming issue as the G4P button simply calls the procedure and should have no involvement in the procedure - that is why I posted it here.

Here's the code:

void loadTemplateData(int Tnum){
String lines[] = loadStrings("Templates/Template"+ Tnum + ".txt");
templateTitle = lines[0];
String sizes[] = split(lines[1], ',');
txtWidth = int(sizes[0]);
txtHeight = int(sizes[1]);
println("Template "+templateTitle+" uses boxes "+txtWidth+" by "+txtHeight+" in the following locations:");
for (int i = 2; i < (lines.length-1); i++) {
String pieces[] = split(lines[i], ',');
println("Line " + (i+1) + " of " + lines.length);
println("Boxes at :" + pieces[0] +" , "+ pieces[1]);
BoxX[i-2] = parseInt(pieces[0]); //commenting out this and the next 2 lines avoids the error
BoxY[i-2] = parseInt(pieces[1]);
println("rectangle location = " + BoxX[i-2] + " , " + BoxY[i-2]);
}
}

and here's the text file it is reading:

Nametags, 8-up

100,100

124,123

124,367

271,367

544,205

544,340

544,475

686,340

686,475

Here's the console output from lines 10, 13 & 14 when the array-filling lines (15,16,17) are commented out, showing that the textfile reading is sound:

Template Nametags, 8-up uses boxes 100 by 100 in the following locations:

Line 3 of 11

Boxes at :124 , 123

Line 4 of 11

Boxes at :124 , 367

Line 5 of 11

Boxes at :271 , 367

Line 6 of 11

Boxes at :544 , 205

Line 7 of 11

Boxes at :544 , 340

Line 8 of 11

Boxes at :544 , 475

Line 9 of 11

Boxes at :686 , 340

Line 10 of 11

Boxes at :686 , 475

Any suggestions/thoughts?

Thanks in advance

Replies(5)

hondaman9..

Re: Exception in event handler error - is it scope?

1 year ago

I mention above that the error refers to the G4P library, but it doesn't. My program working title has "G4P" in it so I can track the version, that's why "G4P" shows up in the error message.

When I call the procedure from elsewhere in the code (not from a G4P button), the same issue persists and I get the following error:

Exception in thread "Animation Thread" java.lang.NullPointerException

at JupiterShowDemo_v6_G4P_b.loadTemplateData(JupiterShowDemo_v6_G4P_b.java:603)

at JupiterShowDemo_v6_G4P_b.setup(JupiterShowDemo_v6_G4P_b.java:110)

at processing.core.PApplet.handleDraw(Unknown Source)

at processing.core.PApplet.run(Unknown Source)

at java.lang.Thread.run(Thread.java:662)

Hope this helps clarify

PhiLho

Re: Exception in event handler error - is it scope?

1 year ago

Hard to tell with just this fragment of code.
Perhaps you can take a look at the article Why do I get a NullPointerException?, hopefully it can lead you to a solution.

hondaman9..

Re: Exception in event handler error - is it scope?

1 year ago

PhiLho, thank you again. You're a great asset and resource to our community and this forum.

I had skimmed that article but was looking at the array stuffing aspects and not the declarations part of my code. I hadn't being specifying the size of the new array as it would vary, but after re-reading the article I tried setting them to 20 elements (I know I'm safe with a ceiling of 20) it works just fine. I'm not sure why that is, but my code seems to require the definition of size when I declare my arrays in this case.

My offending code was:

int[] BoxX;
int[] BoxY;

and the working declaration is now:

int[] BoxX = new int[20];
int[] BoxY = new int[20];

Thank again for your help!

quarks

Re: Exception in event handler error - is it scope?

1 year ago

I'm not sure why that is, but my code seems to require the definition of size when I declare my arrays in this case.

the lines

int[] BoxX;
int[] BoxY;

simply state that you want to make use of 2 integer arrays but it does not create them, so at this stage BoxX and BoxY hold the value null. Attempting to use BoxX and BoxY will cause the NullPointerException, which is what happened.

The lines

int[] BoxX = new int[20];
int[] BoxY = new int[20];

also create the arrays so they can be used.

So in your code above lines 15-17 caused the NPE because the arrays didn't exist.

Additional information about error messages.

G4P (the library) uses a special technique called reflection so that when you click on a button it executes a method called handleButtonEvents. If an exception occurs in any code excuted inside this method or any other method called by this method (such as loadTemplateData) then G4P catches this exception and reports the error e.g.

               #############  EXCEPTION IN EVENT HANDLER  #############
              

               An error occured during execution of the eventhandler:
              

               CLASS: 
               JupiterShowDemo_v6_G4P_b   METHOD: 
               handleButtonEvents
              

                Caused by java.lang.NullPointerException
              

                JupiterShowDemo_v6_G4P_b.loadTemplateData(JupiterShowDemo_v6_G4P_b.java:608)
              

########################################################

This identifies the class and method where the exception occured. This is much more informative than the messaage you would have got if the library allowed the Java reflection classes to handle the exception instead.

PS this post was caught by Zoho's anti spammer - can't see why! It makes you wonder about the skill of Zoho's programmers if they can't create more sophisticated software especially when you see some of the spam posts that slip through. You will get to see this when a moderator clears it.

PhiLho

Re: Re: Exception in event handler error - is it scope?

1 year ago

Indeed... In the thread Spam Issues started by Casey, I told them what I think of their anti-spam techniques...
For laughs, here is why your message was found as spammy:

Special Word Pattern Match :messaage

Don't make typos!

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