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@ThreadSafe
public final class MovablePoint {

  @GuardedBy("this")
    double xPos = 1.0;
  @GuardedBy("this")
    double yPos = 1.0;
  @GuardedBy("itself")
    static final List<MovablePoint> memo = new ArrayList<MovablePoint>();

  public void move(double slope, double distance) {
    synchronized (this) {
      rememberPoint(this);
      xPos += (1 / slope) * distance;
      yPos += slope * distance;
    }
  }

  public static void rememberPoint(MovablePoint value) {
    synchronized (memo) {
      memo.add(value);
    }
  }
}