nullpointerexception question

murmsk

First.... what does this mean? While doing a search I see this error a lot attached to a variety of different sketches.

second I am doing a serial feed read from temperature sensors on an arduino. It runs fine for awhile then throws the nullpointerexception.

steve

Chrisir

when a var is null and you wanna use it it throws this

e.g. you load an image which is not there and then you want to show it.

PImage a1 = loadImage("wrong.png");
image (a1,30,30); // fails 

better

PImage a1 = loadImage("wrong.png");
if (a1!=null) 
    image (a1,30,30); // better

please read on here, section exceptions:

http://wiki.processing.org/w/Technical_FAQ

GoToLoop

That happens when we try to access a property from a null reference. Using the dot operator for example:

http://processing.org/reference/dot.html

Chrisir

you wrote

second I am doing a serial feed read from temperature sensors on an arduino. It runs fine for awhile then throws the nullpointerexception.

I think when the speed of the sensor and your PC don't match, the sensor value can be null (there wasn't a sensor value, buffer was empty) - hence the error

to avoid this, check your sensor data if they are null:

if (sensor1 != null)
    {
       // do something 
    }

also look at try---catch....

PhiLho

See Technical FAQ in the Exceptions section for general explanations, and more specifically: Why do I get a NullPointerException?