How do I get Arduino to communicate with Processing? - arduino

Question

I wanted to make my Arduino communicate with Processing.
On Arduino, I use the code taken from the Processing site (Example 1A):
int switchPin = 4; // Switch connected to pin 4
void setup()
{
pinMode(switchPin, INPUT); // Set pin 0 as an input
Serial.begin(9600); // Initialize serial communications at a 9600 baud rate
}
void loop()
{
if (digitalRead(switchPin) == HIGH) // If switch is ON,
// send 1 to Processing
{
Serial.write(1);
}
else
{ // If the switch is not ON,
Serial.write(0); // send 0 to Processing
}
delay(100);
}
While in Processing I use this code:
import processing.serial.*;
Serial myPort; // Create object from Serial class
String val = "0"; // Data received from the serial port
void setup()
{
size(200, 200);
frameRate(10);
String portName = Serial.list()[0]; // Change the 0 to a 1, 2,
// etc. to match your port.
myPort = new Serial(this, portName, 9600);
}
void draw()
{
if (myPort.available() > 0)
{
// If data is available,
val = myPort.readStringUntil('\n'); // Read it and store it in val
}
background(255);
if(val.equals("0"))
{
fill(0);
}
else
{
fill(204);
}
rect(50, 50, 100, 100);
}
The program gives me the error NullPointerException on line 22 in the Processing program.
How can I solve it?

Answer 1

There is a delay in the communication and it is possible that the first time when the draw function is called, the serial port doesn't send any data, and the value received is null. That might be the reason you get the NullPointerException.
Try this:
void draw()
{
while (myPort.available() > 0)
{
// If data is available,
val = myPort.readStringUntil('\n'); // Read it and store it in val
}
background(255);
if(val != null)
{
if(val.equals("0"))
{
fill(0);
}
else
{
fill(204);
}
}
rect(50, 50, 100, 100);
}