//
// HelloWeb4 applet example.
// Source:  _Exploring Java_, Niemeyer & Peck.
// Modified by:  B. Massingill.
//
// Description:
//      A HelloWeb4 applet displays an environment-selected message 
//      and allows the user to drag it around with the mouse.
//      It also provides a "change color" button that, when clicked,
//      changes the color of the message, cycling through a 
//      pre-defined list of colors.  The message blinks while the
//      enclosing window is visible.
//
// Usage:
//      Applet tag parameter "message" gives message to display.
//      Requires window sufficiently large to display selected
//              message, starting at position (125, 95).
//      Responds to click-and-drag operations on displayed messages.
//      Responds to button clicks.
//
import java.applet.Applet ;
import java.awt.* ;
import java.awt.event.* ;
import java.io.* ;

public
class HelloWeb4
extends Applet 
implements MouseMotionListener, ActionListener, Runnable {

        int messageX = 125, messageY = 95 ;
        String theMessage ;
        Button theButton ;
        int colorIndex = 0 ;
        static Color[] someColors = {
                Color.black, Color.red, Color.green,
                Color.blue, Color.magenta
                } ;
        Thread blinkThread ;
        boolean blinkState ;

        // ---- overridden superclass methods --------------------------

        // init:  get message, set things up.
        public void
        init() {
                theMessage = getParameter("message") ;

                // create "change color" button.
                theButton = new Button("Change Color") ;
                add(theButton) ;

                // set up to process mouse and button events.
                addMouseMotionListener(this) ;
                theButton.addActionListener(this) ;
        }

        // paint:  set color based on blinkState (changed by
        //      blinkThread, display message at current location.
        public void 
        paint(Graphics gc) {
                gc.setColor(blinkState ? Color.white : currentColor()) ;
                gc.drawString(theMessage, messageX, messageY) ;
        }

        // ---- methods to handle mouse events -------------------------

        // respond to "mouse dragged" events by changing location
        //      of displayed message.
        public void
        mouseDragged(MouseEvent e) {
                messageX = e.getX() ;
                messageY = e.getY() ;
                repaint() ;
        }

        // ignore "mouse moved" events.
        public void
        mouseMoved(MouseEvent e) {
        }

        // ---- methods to handle button events ------------------------

        // respond to click on "change color" button.
        public void
        actionPerformed(ActionEvent e) {
                if (e.getSource() == theButton) changeColor() ;
        }

        // ---- methods to set, obtain current color for message -------
        //      synchronized to avoid simultaneous access to colorIndex
        //      by changeColor and currentColor.

        // changeColor:  reset foreground color, repaint.
        synchronized private void
        changeColor() {
                if (++colorIndex == someColors.length) colorIndex = 0 ;
                setForeground(currentColor()) ;
                repaint() ;
        }

        synchronized private Color
        currentColor() {
                return someColors[colorIndex] ;
        }

        // ---- method for thread that produces blink effect -----------

        // run:  every 500 millisecs, toggle blinkState and repaint.
        public void
        run() {
                while (true) {
                        blinkState = !blinkState ;
                        repaint() ;
                        try {
                                Thread.sleep(500) ;
                        } catch (Exception e) {
                        }
                }
        }

        // ---- more overridden superclass methods ---------------------

        // start:  if no blink thread, create one.
        public void
        start() {
                if (blinkThread == null) {
                        blinkThread = new Thread(this) ;
                        blinkThread.start() ;
                        System.out.println("starting blink thread") ;
                }
        }

        // stop:  if blink thread, stop it and delete it.
        public void
        stop() {
                if (blinkThread != null) {
                        blinkThread.stop() ;
                        blinkThread = null ;    
                                // object formerly referenced by
                                // blinkThread now subject to 
                                // garbage collection
                        System.out.println("stopping blink thread") ;
                }
        }
}