I'm using a Processing user interface to control a robot via bluetooth. I get "Exception in thread "Animation Thread" java.lang.NullPointerException
     at GUI$Bluetooth.checkTestButtonClick(GUI.java:231)
     at GUI.mousePressed(GUI.java:101)
     at processing.core.PApplet.handleMouseEvent(PApplet.java:1607)
     at processing.core.PApplet.dequeueMouseEvents(PApplet.java:1544)
     at processing.core.PApplet.handleDraw(PApplet.java:1436)
     at processing.core.PApplet.run(PApplet.java:1327)
     at java.lang.Thread.run(Thread.java:613)"

Note that I only get this error when I click the forward button, not when it is launched.

Line 231 is "void drawBt()", which is the method that draws everything to be used by thr Bluetooth:

Code:

void drawBt() //Draws all things related to bluetooth
  {
    
    if (testButtonMouseOver)
    {
     fill(0, 102, 153);
    }
     PFont font;
     font = loadFont("BankGothic-Light-20.vlw");
     textFont(font);
     text("Test LED", BLUETOOTH_TEST_BUTTON_Label_X, BLUETOOTH_TEST_BUTTON_Label_Y); 
     rect(BLUETOOTH_TEST_BUTTON_X, BLUETOOTH_TEST_BUTTON_Y, STANDARD_BUTTON_WIDTH, STANDARD_BUTTON_HEIGHT); //Draw Bluetooth Test button
     //fill(STANDARD_BUTTON_COLOR); //Fill button
     
     text("Left", BLUETOOTH_LEFT_BUTTON_LABEL_X, BLUETOOTH_LEFT_BUTTON_LABEL_Y); 
     rect(BLUETOOTH_LEFT_BUTTON_X, BLUETOOTH_LEFT_BUTTON_Y, STANDARD_BUTTON_WIDTH, STANDARD_BUTTON_HEIGHT);
     
     text("Right", BLUETOOTH_RIGHT_BUTTON_LABEL_X, BLUETOOTH_RIGHT_BUTTON_LABEL_Y); 
     rect(BLUETOOTH_RIGHT_BUTTON_X, BLUETOOTH_RIGHT_BUTTON_Y, STANDARD_BUTTON_WIDTH, STANDARD_BUTTON_HEIGHT);
     
     text("Forward", BLUETOOTH_FORWARD_BUTTON_LABEL_X, BLUETOOTH_FORWARD_BUTTON_LABEL_Y); 
     rect(BLUETOOTH_FORWARD_BUTTON_X, BLUETOOTH_FORWARD_BUTTON_Y, STANDARD_BUTTON_WIDTH, STANDARD_BUTTON_HEIGHT);
     
     // DRAW RADAR STUFF
     
     //ellipse(RADAR_X, RADAR_Y, RADAR_WIDTH, RADAR_HEIGHT);
     
     //fill(0);
     //ellipse(RADAR_X, RADAR_Y, RADAR_CENTER_HEIGHT, RADAR_CENTER_WIDTH);
     //fill(255);
     
     //r.draw();
    
  }
 

Here's a sample from the checkMouseClick() method:

Code:

void checkTestButtonClick()
  {
    //println("Button Click Tested!");
    
    if (mouseX > BLUETOOTH_TEST_BUTTON_X && mouseX < BLUETOOTH_TEST_BUTTON_X + STANDARD_BUTTON_WIDTH &&
    mouseY > BLUETOOTH_TEST_BUTTON_Y && mouseY <  BLUETOOTH_TEST_BUTTON_Y + STANDARD_BUTTON_HEIGHT)
    {
	println("Test Button CLicked!");
	
	myPort.write('A'); // Sends 'A' char to on board computer to be processed and interpreted
	delay(TIME_BEFORE_RESET);
	myPort.write('Z');
    }
 

This is the robot's code:

Code:

char val; // Data received from the serial port
int ledPin = 13; // Set the pin to digital I/O 4

int leftMotorPin = 8;
int rightMotorPin = 9;

void setup() {
pinMode(ledPin, OUTPUT); // Set pin as OUTPUT
Serial.begin(115200); // Start serial communication at 9600 bps

//Declare the purpose and use of pin 8 and 9 for motors (output)
pinMode(8, OUTPUT);
pinMode(9, OUTPUT);
}

void loop() {
if (Serial.available()) { // If data is available to read,
val = Serial.read(); // read it and store it in val
}
if (val == 'A') { // If A was received
digitalWrite(ledPin, HIGH); // turn the LED on
delay(400);
digitalWrite(ledPin, LOW); // turn the LED on
}
else {
digitalWrite(ledPin, LOW); // Otherwise turn it OFF
}

if (val == 'B') //If Left Motor activated
{
  digitalWrite(leftMotorPin, HIGH);
  delay(1000);
  digitalWrite(leftMotorPin, LOW);
}
else
{
  digitalWrite(leftMotorPin, LOW);
}

if (val == 'C') //If right Motor activated
{
  digitalWrite(rightMotorPin, HIGH);
  delay(1000);
  digitalWrite(rightMotorPin, LOW);
}
else
{
  digitalWrite(rightMotorPin, LOW);
}

if (val == 'D') //If right and left Motor activated
{
  digitalWrite(rightMotorPin, HIGH);
  digitalWrite(leftMotorPin, HIGH);
  
  delay(1000);
  
  digitalWrite(rightMotorPin, LOW);
  digitalWrite(leftMotorPin, LOW);
}
else
{
  digitalWrite(rightMotorPin, LOW);
  digitalWrite(leftMotorPin, LOW);
}

if (val == 'Z') //If right and left Motor activated
{
  digitalWrite(rightMotorPin, LOW);
  digitalWrite(leftMotorPin, LOW);
}

delay(10); // Wait 100 milliseconds for next reading
}
 

The bluetooth blinks red, showing that it is on, however it does not turn green when GUI is launched. This means that a Bluetooth connection was never established. Can someone help me figure out why?

koogy is right, the stack trace gives an hint where the problem happens: in the checkTestButtonClick() method.
Fortunately, it is quite short, so I can guess you have the issue because myPort is null.

You get a portName, but how do you use it? How myPort is created? That's the one which is null, not portName.