Why do I get a NullPointerException

[LauraDob]

When I run it, I have NullPointerException [0] “COM5”… How do I fix it? This is the code

import processing.serial.*;
Serial myPort; // Create object from Serial class
int val = 0;
int oldval = 0;
int numFrames = 2;
int frame = 0;
PImage img;
PImage[] images = new PImage[numFrames];

void setup()
{
size (1500, 1500);
images[0] = loadImage(“fase1.jpg”);
images[1] = loadImage(“fase2.jpg”);
printArray(Serial.list());
myPort = new Serial(this, “COM5”, 9600);
}
void draw()
{
if (myPort.available() > 0) {
val = myPort.read();
}
if (val != oldval && val == 2) {
if (frame<numFrames-1) {
frame = (frame+1);
} else {
frame = 0;
}
}
image(img, 0, 0);
oldval = val;
}

[Chrisir]

Check kll’s post here: Unable to receive serial data from Arduino - #3 by kll

[JSGauthier]

Hi there,
It is likely that you you are referencing a serial port that returns ‘null’. This means there is nothing listed as COM5.
Perhaps if you comment out //myPort = new Serial(this. “COM5”, 9600);
then read the print out in the console of the previous line -
printArray(Serial.list());
You may then
-replace Com5 with a different value from the list and see if you code runs.
or
You can check if COM5 is listed with different syntax.

Hope this helps.
Cheers,
jsg

[LauraDob]

Hi thank you for your help but i’m 100% certain that it is COM5. So that’s not it

[glv]

Hello @LauraDob,

Please format your code as a courtesy to this forum:
https://discourse.processing.org/faq#format-your-code

You did not load an image and are trying to display it so it gives an error.

Here is an MCVE:

Try displaying one of these images which you have loaded:

images[0] = loadImage("fase1.jpg");
images[1] = loadImage("fase2.jpg");

Reference:
Why do I get a NullPointerException? - Processing 2.x and 3.x Forum

I do not have a "COM 5" and I get a RuntimeException for that:

:)

[JSGauthier]

Hi @LauraDob,

I think I can see the error here. (Your insistance on COM5 being the right port was a good hint). Since you are certain that you want to reference “COM5” then you must refer to “COM5” via the address Serial.list()[index] (here the index is the value for “COM5” that is printed when you check the console following this line: printArray(Serial.list());

The console should tell you which Serial.list()[index to put].

(on my computer it prints: [0] “COM3”, it should list others like COM 5 also…)

So try changing your reference argument in Serial to something like this…

myPort = new Serial(this, Serial.list()[place the index # here], 9600);

Hope this helps.

Cordially,
JS

PS: Check the example files for the Serial Library for more hints on syntax for the Serial library.

[glv]

Hello,

The error in the code from @LauraDob in this case is because img is null.

A minimal example:

import processing.serial.*;
Serial myPort; // Create object from Serial class

PImage img;
String url = "https://media.digikey.com/Renders/Stackpole%20Renders/RC12-56Ohm-5_tmb.jpg";

void setup()
  {
  size (100, 100);
  printArray(Serial.list());
  
  // Either one of these will work:
  myPort = new Serial(this, "COM9", 9600);
  //myPort = new Serial(this, Serial.list()[0], 9600);
  
  //img = loadImage(url); //It works with this uncommented
  }

void draw()
  {
  image(img, 18, 18);
  }

"COM9" is my Arduino COM port.

  // Either one of these will work and can be interchanged:
  myPort = new Serial(this, "COM9", 9600);
  //myPort = new Serial(this, Serial.list()[0], 9600);

This is the error if you did not load an image:

It works if you load an image.

:)

[JSGauthier]

Thanks @glv,
Your care and attention to detail is appreciated. I’ll task myself to apply that same care in my responses moving forward. Keep up the kind work!