I am working on a simple game for my class involving cars that move down the screen towards a player.
It uses graphics and a midi controller for input so sorry if it becomes hard to test the code yourself.

The problem I am having is with the car collision.
I want the cars on collision to reset to their starting positions but cant seem to work it out.
I would also like for the other cars to start in a random position each time (and preferably not on top of each other)  but the code I implemented only does this for the first instance of the cars.
any help much appreciated.


import themidibus.*; //MIDIライブラリの読み込み

MidiBus myBus; // The MidiBus
int[] val = new int[4];
int player_x = 500;
int player_y = 500;
int player_w = 10;
int player_h = 10;
int score = 10;

int x;
int xRandom;

PImage bg;
PImage car;
PImage player;
PImage bus;
PImage truck;
Car car1;
Car car2;
Car car3;

//  Define car dimensions.
final int TRUCK_WIDTH = 60;
final int TRUCK_HEIGHT = 360;
int truck_position_x = 125;
int truck_position_y = 50;
final int CAR_WIDTH = 50;
final int CAR_HEIGHT = 100;
int car_position_x = 185;
int car_position_y = 50;
final int BUS_WIDTH = 60;
final int BUS_HEIGHT = 160;
int bus_position_x = 240;
int bus_position_y = 50;

void setup() {
  size(600,800);
  colorMode(HSB,100);
  //background(0);
  bg = loadImage("background.png");
  player = loadImage("f1.png");
  truck = loadImage("truck.png");
  bus = loadImage("bus.png");
  car = loadImage("car.png");
  xRandom = (int)random(125, 250);
  car1 = new Car(truck, xRandom, truck_position_y, TRUCK_WIDTH, TRUCK_HEIGHT, 1);
  car2 = new Car(bus, xRandom, bus_position_y, BUS_WIDTH, BUS_HEIGHT, 2);
  car3 = new Car(car, xRandom, car_position_y, CAR_WIDTH, CAR_HEIGHT, 3);
  smooth();
  MidiBus.list(); //MIDIデバイス一覧の表示
  myBus = new MidiBus(this, 0, 3);//通信用オブジェクトの生成
}

void draw(){
  background(bg);
  strokeWeight(4);
  stroke(255,247,3);
  //////////////////////
  //fill(0);
  for(int i = 14; i<width; i+=14) {
    noStroke();
    fill(190);
    rect (i,height/2.6,7,4);
  }
  ///////////////////////
  for(int i = 14; i<width; i+=14) {
    noStroke();
    fill(190);
    rect (i,height/1.6,7,4);
  }
  //////////////////////
  car1.draw();
  car1.move();
  car2.draw();
  car2.move();
  car3.draw();
  car3.move();

  player();
}

void player(){
  fill(10,50,100);
  player_x = (width - player_h) * val[3] / 127;
  image(player, player_x, player_y);

}


void noteOn(int channel, int pitch, int velocity) {
// データが読み込まれたときに呼び出される関数
// chanel 0: X方向
// chanel 1: Y方向
// chanel 2: X方向
// chanel 3: ボリューム
         val[channel] = velocity; 
/*    println();
    println("Note On:");
    println("--------");
    println("Channel:"+channel);
    println("Pitch:"+pitch);
    println("Velocity:"+velocity);
*/

}

class Car
{
  PImage carImage;
  int x, y, w, h;
  int speed;
 
  Car(PImage c, int x, int y, int w, int h, int s)
  {
    this.carImage = c;
    this.x = x;
    this.y = y;
    this.w = w;
    this.h = h;
    this.speed = s;
  }
 
  void draw()
  {
    noStroke();
    rect(this.x, this.y, this.w, this.h);
    image(this.carImage, this.x, this.y);
    hitCheck(this.x, this.y, this.w, this.h);
  }
 
  void move()
  {
    this.y += this.speed;
    if (this.y > height) {
      this.y = 0;
    }
  }
}

void hitCheck(int x, int y, int h, int w){
  if( x + (w) >= player_x &&
      y + (h) >= player_y &&
      x  <= player_x + player_w &&
      y  <= player_y + player_h){
      score = score + 10;
      println (score);
      }
}