https://learn.sparkfun.com/tutorials/connecting-arduino-to-processing/all

import processing.serial.*;
import cc.arduino.*;
Serial myPort;
Arduino arduino;

void setup () {
  println(Arduino.list());
  arduino = new Arduino(this, Arduino.list() [1], 57600);
  arduino.pinMode(12, Arduino.OUTPUT);
  arduino.pinMode(11, Arduino.OUTPUT);
  arduino.pinMode(9, Arduino.OUTPUT);
  arduino.pinMode(10, Arduino.OUTPUT);
}

void draw() {
  if (keyPressed == true) {
    if (key == 'w' || key == 'W') {
      arduino.digitalWrite (2, Arduino.HIGH);
    }
    if (key == 's' || key == 'S') {
      arduino.digitalWrite (7, Arduino.HIGH);
    }
    if (key == 'a' || key == 'A') {
      arduino.digitalWrite (8, Arduino.HIGH);
    }
    if (key == 'd' || key == 'D') {
      arduino.digitalWrite (10, Arduino.HIGH);
    }}
    else {
      arduino.digitalWrite (2, Arduino.LOW);
      arduino.digitalWrite (7, Arduino.LOW);
      arduino.digitalWrite (8, Arduino.LOW);
      arduino.digitalWrite (10, Arduino.LOW);
    }}