Plotter.cls

public class Plotter {

  class Point {
      Double x;
      Double y;

      Point(Double x, Double y) {
           this.x = x;
           this.y = y;
      }
      Double getXCoordinate() {
           return x;
      }

      Double getYCoordinate() {
           return y;
      }
  }

  static List<Point> points = new List<Point>();

  static public void plot(Double x, Double y) {
      points.add(new Point(x, y));
  }
  
  static public void render() {
    System.debug(points);
  }
}