import javax.swing.*;
import java.awt.*;
import java.awt.geom.*;

public class CurveApplet extends JApplet
{
  // Initialize the applet
  public void init()
  {
    pane = new CurvePane();                   // Create pane containing curves
    Container content = getContentPane();     // Get the content pane

    // Add the pane displaying the curves to the content pane for the applet
    content.add(pane);                 // BorderLayout.CENTER is default position
  }

  // Class defining a pane on which to draw
  class CurvePane extends JComponent
  {
    // Constructor
    public CurvePane()
    {
      quadCurve = new QuadCurve2D.Double(                // Create quadratic curve
                       startQ.x, startQ.y,               // Segment start point
                       control.x, control.y,             // Control point
                       endQ.x, endQ.y);                  // Segment end point

      cubicCurve = new CubicCurve2D.Double(              // Create cubic curve
                       startC.x, startC.y,               // Segment start point
                       controlStart.x, controlStart.y,   // Control point for start
                       controlEnd.x, controlEnd.y,       // Control point for end
                           endC.x, endC.y);              // Segment end point
    }
    public void paint(Graphics g)
    {
      Graphics2D g2D = (Graphics2D)g;                    // Get a 2D device context

      // Draw the curves
      g2D.setPaint(Color.blue);
      g2D.draw(quadCurve);
      g2D.draw(cubicCurve);

      // Create and draw the markers showing the control points
      g2D.setPaint(Color.red);                   // Set the color
      ctrlQuad.draw(g2D);                       
      ctrlCubic1.draw(g2D);
      ctrlCubic2.draw(g2D);

      // Draw tangents from the curve end points to the control marker centers
      Line2D.Double tangent = new Line2D.Double(startQ, ctrlQuad.getCenter());
      g2D.draw(tangent);
      tangent = new Line2D.Double(endQ, ctrlQuad.getCenter());
      g2D.draw(tangent);
      tangent = new Line2D.Double(startC, ctrlCubic1.getCenter());
      g2D.draw(tangent);
      tangent = new Line2D.Double(endC, ctrlCubic1.getCenter());
      g2D.draw(tangent);
      tangent = new Line2D.Double(startC, ctrlCubic2.getCenter());
      g2D.draw(tangent);
      tangent = new Line2D.Double(endC, ctrlCubic2.getCenter());
      g2D.draw(tangent);
    }
  }

  // Inner class defining a control point marker
  class Marker
  {
    public Marker(Point2D.Double control)
    {
      center = control;                   // Save control point as circle center

      // Create circle around control point
      circle = new Ellipse2D.Double(control.x-radius, control.y-radius,
                                    2.0*radius, 2.0*radius); 
    }

    // Draw the marker
    public void draw(Graphics2D g2D)
    {
      g2D.draw(circle);
    }

   // Get center of marker - the control point position
    Point2D.Double getCenter()
    {
      return center;
    }

    Ellipse2D.Double circle;               // Circle around control point
    Point2D.Double center;                 // Circle center - the control point
    static final double radius = 3;        // Radius of circle
  }

  // Points for quadratic curve
  Point2D.Double startQ = new Point2D.Double(50, 150);         // Start point
  Point2D.Double endQ = new Point2D.Double(150, 150);          // End point
  Point2D.Double control = new Point2D.Double(80, 100);        // Control point

  // Points for cubic curve
  Point2D.Double startC = new Point2D.Double(50, 300);         // Start point
  Point2D.Double endC = new Point2D.Double(150, 300);          // End point
  Point2D.Double controlStart = new Point2D.Double(80, 250);   // 1st control point
  Point2D.Double controlEnd = new Point2D.Double(160, 250);    // 2nd control point

  // Markers for control points
  Marker ctrlQuad = new Marker(control);
  Marker ctrlCubic1 = new Marker(controlStart);
  Marker ctrlCubic2 = new Marker(controlEnd);

  QuadCurve2D.Double quadCurve;                        // Quadratic curve
  CubicCurve2D.Double cubicCurve;                      // Cubic curve
  CurvePane pane = new CurvePane();                    // Pane to contain curves
}