Null pointer exception on Processing (ldrValues) - nullpointerexception

Question

My code involves both Processing and Arduino. 5 different photocells are triggering 5 different sounds. My sound files play only when the ldrvalue is above the threshold.
The Null Pointer Exception is highlighted on this line
for (int i = 0; i < ldrValues.length; i++) {
I am not sure which part of my code should be changed so that I can run it.
import processing.serial.*;
import processing.sound.*;
SoundFile[] soundFiles = new SoundFile[5];
Serial myPort; // Create object from Serial class
int[] ldrValues;
int[] thresholds = {440, 490, 330, 260, 450};
int i = 0;
boolean[] states = {false, false, false, false, false};
void setup() {
size(200, 200);
println((Object[])Serial.list());
String portName = Serial.list()[3];
myPort = new Serial(this, portName, 9600);
soundFiles[0] = new SoundFile(this, "1.mp3");
soundFiles[1] = new SoundFile(this, "2.mp3");
soundFiles[2] = new SoundFile(this, "3.mp3");
soundFiles[3] = new SoundFile(this, "4.mp3");
soundFiles[4] = new SoundFile(this, "5.mp3");
}
void draw()
{
background(255);
//serial loop
while (myPort.available() > 0) {
String myString = myPort.readStringUntil(10);
if (myString != null) {
//println(myString);
ldrValues = int(split(myString.trim(), ','));
//println(ldrValues);
}
}
for (int i = 0; i < ldrValues.length; i++) {
println(states[i]);
println(ldrValues[i]);
if (ldrValues[i] > thresholds[i] && !states[i]) {
println("sensor " + i + " is activated");
soundFiles[i].play();
states[i] = true;
}
if (ldrValues[i] < thresholds[i]) {
println("sensor " + i + " is NOT activated");
soundFiles[i].stop();
states[i] = false;
}
}
}

Answer 1

You're approach is shall we say optimistic ? :)
It's always assuming there was a message from Serial, always formatted the right way so it could be parsed and there were absolutely 0 issues buffering data (incomplete strings, etc.))
The simplest thing you could do is check if the parsing was successful, otherwise the ldrValues array would still be null:
void draw()
{
background(255);
//serial loop
while (myPort.available() > 0) {
String myString = myPort.readStringUntil(10);
if (myString != null) {
//println(myString);
ldrValues = int(split(myString.trim(), ','));
//println(ldrValues);
}
}
// double check parsing int values from the string was successfully as well, not just buffering the string
if(ldrValues != null){
for (int i = 0; i < ldrValues.length; i++) {
println(states[i]);
println(ldrValues[i]);
if (ldrValues[i] > thresholds[i] && !states[i]) {
println("sensor " + i + " is activated");
soundFiles[i].play();
states[i] = true;
}
if (ldrValues[i] < thresholds[i]) {
println("sensor " + i + " is NOT activated");
soundFiles[i].stop();
states[i] = false;
}
}
}else{
// print a helpful debugging message otherwise
println("error parsing ldrValues from string: " + myString);
}
}
(Didn't know you could parse a int[] with int(): nice!)