src/main/java/chalmers/pimp/model/LayerMovement.java
void start(int x, int y, ModelMemento memento) {
    Objects.requireNonNull(memento);
    if (!isFinished) {
      prevX = x;
      prevY = y;
      this.memento = Objects.requireNonNull(memento);
    }
  }
/**
   * Starts the layer movement. This method has no effect if the {@link LayerMovement#stop()} method
   * has been called on the layer movement instance.
   *
   * @param x       the current x-coordinate of the layer.
   * @param y       the current y-coordinate of the layer.
   * @param memento a model memento instance that represents the state of the model before the
   *                movement has begun.
   * @throws NullPointerException if the supplied model memento is {@code null}.
   */
Starts the layer movement. This method has no effect if the  LayerMovement#stop() method
has been called on the layer movement instance.

@param x       the current x-coordinate of the layer.
@param y       the current y-coordinate of the layer.
@param memento a model memento instance that represents the state of the model before the
movement has begun.
@throws NullPointerException if the supplied model memento is  null.
Starts the layer movement . This method has no effect if the LayerMovement#stop () method has been called on the layer movement instance . @param x the current x - coordinate of the layer . @param y the current y - coordinate of the layer . @param memento a model memento instance that represents the state of the model before the movement has begun . @throws NullPointerException if the supplied model memento is null .
void start(int x, int y, ModelMemento memento) {
    Objects.requireNonNull(memento);
    if (!isFinished) {
      prevX = x;
      prevY = y;
      this.memento = Objects.requireNonNull(memento);
    }
  }
void start ( int x , int y , ModelMemento memento ) { Objects . requireNonNull ( memento ) ; if ( ! isFinished ) { prevX = x ; prevY = y ; this . memento = Objects . requireNonNull ( memento ) ; } }
Starts the layer movement.
Starts the layer movement .