gistfile1.java

class Car {
  Door leftDoor, rightDoor;
  Wheel leftFrontWheel, leftRearWheel, rightFrontWheel, rightRearWheel;

  Car() {
    Door leftDoor = new Door(true, false);
    Door rightDoor 
    // other constructor things...

    rightDoor.open();
  }
}

class Door {
  // instance variables describing a door go here

  Door(boolean locking, boolean window) {
    // construct a door here!
  }

  void open() {
    // opens door
  }
}