import javax.swing.*;

 import java.awt.*;

 import java.awt.geom.*;

 import javax.swing.event.MouseInputAdapter;

 import java.awt.event.MouseEvent;

 @SuppressWarnings("serial")

 public class CurveApplet extends JApplet {

   // Initialize the applet

   @Override

   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

   MouseHandler handler = new MouseHandler();                           // Create the listener

   pane.addMouseListener(handler);                                      // Monitor mouse button presses

   pane.addMouseMotionListener(handler);                                // as well as movement

   }

   // 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 pt for start

                       controlEnd.x, controlEnd.y,                      // Control point for end

                       endC.x, endC.y);                                 // Segment end point

     }

     @Override

     public void paint(Graphics g) {

       Graphics2D g2D = (Graphics2D)g;                                  // Get a 2D device context

       // Update the curves with the current control point positions

       quadCurve.ctrlx = ctrlQuad.getCenter().x;

       quadCurve.ctrly = ctrlQuad.getCenter().y;

       cubicCurve.ctrlx1 = ctrlCubic1.getCenter().x;

       cubicCurve.ctrly1 = ctrlCubic1.getCenter().y;

       cubicCurve.ctrlx2 = ctrlCubic2.getCenter().x;

       cubicCurve.ctrly2 = ctrlCubic2.getCenter().y;

       // 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, ctrlCubic2.getCenter());

       g2D.draw(tangent);

     }

   }

   // Inner class defining a control point marker

   private 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;

     }

     // Test if a point x,y is inside the marker

     public boolean contains(double x, double y) {

       return circle.contains(x,y);

     }

     // Sets a new control point location

     public void setLocation(double x, double y) {

       center.x = x;                      // Update control point

       center.y = y;                      // coordinates

       circle.x = x-radius;               // Change circle position

       circle.y = y-radius;               // correspondingly

     }

     Ellipse2D.Double circle;                                           // Circle around control point

     Point2D.Double center;                                             // Circle center - the control point

     static final double radius = 3;                                    // Radius of circle

   }

   private class MouseHandler extends MouseInputAdapter {

     @Override

     public void mousePressed(MouseEvent e) {

       // Check if the cursor is inside any marker

       if(ctrlQuad.contains(e.getX(), e.getY()))

         selected = ctrlQuad;

       else if(ctrlCubic1.contains(e.getX(), e.getY()))

         selected = ctrlCubic1;

       else if(ctrlCubic2.contains(e.getX(), e.getY()))

         selected = ctrlCubic2;

     }

     @Override

     public void mouseReleased(MouseEvent e) {

       selected = null;                                                 // Deselect any selected marker

     }

     @Override

     public void mouseDragged(MouseEvent e) {

       if(selected != null) {                                           // If a marker is selected

         // Set the marker to current cursor position

         selected.setLocation(e.getX(), e.getY());

         pane.repaint();                                                // Redraw pane contents

       }

     }

     private Marker selected;                                           // Stores reference to selected marker

   }

   // Points for quadratic curve

   private Point2D.Double startQ = new Point2D.Double(50, 75);          // Start point

   private Point2D.Double endQ = new Point2D.Double(150, 75);           // End point

   private Point2D.Double control = new Point2D.Double(80, 25);         // Control point

   // Points for cubic curve

   private Point2D.Double startC = new Point2D.Double(50, 150);         // Start point

   private Point2D.Double endC = new Point2D.Double(150, 150);          // End point

   private Point2D.Double controlStart = new Point2D.Double(80, 100);   // 1st cntrl point

   private Point2D.Double controlEnd = new Point2D.Double(160, 100);    // 2nd cntrl point

   private QuadCurve2D.Double quadCurve;                                // Quadratic curve

   private CubicCurve2D.Double cubicCurve;                              // Cubic curve

   private CurvePane pane = new CurvePane();                            // Pane to contain curves

    // Markers for control points

    private Marker ctrlQuad = new Marker(control);

    private Marker ctrlCubic1 = new Marker(controlStart);

    private Marker ctrlCubic2 = new Marker(controlEnd);

 }