You are attempting to construct your Talon and Joystick objects too many times. Try constructing them just once in robotInit().
Code:
Joystick mXboxController; // this will drive the robot
Joystick controlStick; // this will be for function of the robot such as toggle the conveyor belt and etc.
Talon frontLeft;
Talon frontRight;
Talon rearRight;
Talon rearLeft;
public void robotInit() { // this code will be ran each time we power on the robot
// Construct joysticks here
mXboxController = new Joystick(0); // depends on the usb connected to computer
controlStick = new Joystick(1);
// Construct Talons here
frontLeft = new Talon(3);
frontRight = new Talon(2);
rearLeft = new Talon(0);
rearRight = new Talon(1);
}
Hope that helps.