mod12ans.lst

Mcgraw-Hill - Java 2 - A Beginner S Guide, 2Nd Ed - 2003 -prog.

listing 1
/* A simple banner applet that uses parameters. 
  
*/  
import java.awt.*;  
import java.applet.*;  
/*  
<applet code="ParamBanner" width=300 height=50>  
<param name=message value=" I like Java! ">  
<param name=delay value=500>  
</applet>  
*/  
  
public class ParamBanner extends Applet implements Runnable {  
  String msg; 
  int delay;  
  Thread t;  
  boolean stopFlag;  
  
  // Initialize t to null.   
  public void init() {  
    String temp; 
 
    msg = getParameter("message");  
    if(msg == null) msg = " Java Rules the Web ";  
  
    temp = getParameter("delay");  
    try {  
      if(temp != null)  
        delay = Integer.parseInt(temp);  
      else  
        delay = 250; // default if not specified 
    } catch(NumberFormatException exc) {  
        delay = 250 ; // default on error 
    }  
     
    t = null;  
  }  
  
  // Start thread  
  public void start() {  
    t = new Thread(this);  
    stopFlag = false;  
    t.start();  
  }  
  
  // Entry point for the thread that runs the banner.  
  public void run() {  
    char ch;  
  
    // Display banner   
    for( ; ; ) {  
      try {  
        repaint();  
        Thread.sleep(delay);  
        ch = msg.charAt(0);  
        msg = msg.substring(1, msg.length());  
        msg += ch;  
        if(stopFlag)  
          break;  
      } catch(InterruptedException exc) {}  
    }  
  }  
  
  // Pause the banner.  
  public void stop() {  
    stopFlag = true;  
    t = null;  
  }  
  
  // Display the banner.  
  public void paint(Graphics g) {  
    g.drawString(msg, 50, 30);  
  }  
}

listing 2
// A simple clock applet. 
 
import java.util.*; 
import java.awt.*;  
import java.applet.*;  
/*  
<object code="Clock" width=200 height=50>  
</object>  
*/  
  
public class Clock extends Applet implements Runnable {  
  String msg; 
  Thread t;  
  Calendar clock; 
 
  boolean stopFlag;  
  
  // Initialize 
  public void init() {  
    t = null;  
    msg = ""; 
  }  
  
  // Start thread  
  public void start() {  
    t = new Thread(this);  
    stopFlag = false; 
    t.start();  
  }  
  
  // Entry point for the clock. 
  public void run() {  
    // Display clock   
    for( ; ; ) {  
      try {  
        clock = Calendar.getInstance(); 
        msg = "Current time is " + 
              Integer.toString(clock.get(Calendar.HOUR));  
        msg = msg + ":" + 
              Integer.toString(clock.get(Calendar.MINUTE)); 
        msg = msg + ":" + 
              Integer.toString(clock.get(Calendar.SECOND)); 
        repaint();  
        Thread.sleep(1000);  
        if(stopFlag)  
          break;  
      } catch(InterruptedException exc) {}  
    }  
  }  
  
  // Pause the clock.  
  public void stop() {  
    stopFlag = true;  
    t = null;  
  }  
  
  // Display the clock.  
  public void paint(Graphics g) {  
    g.drawString(msg, 30, 30);  
  }  
}

listing 3
/* Track mouse motion by drawing a line 
   when a mouse button is pressed. */ 
 
import java.awt.*;  
import java.awt.event.*;  
import java.applet.*;  
/*  
  <applet code="TrackM" width=300 height=100>  
  </applet>  
*/  
  
public class TrackM extends Applet  
  implements MouseListener, MouseMotionListener {  
  
  int curX = 0, curY = 0; // current coordinates 
  int oldX = 0, oldY = 0; // previous coordinates 
  boolean draw; 
  
  public void init() {  
     addMouseListener(this);  
     addMouseMotionListener(this);  
     draw = false; 
  }  
 
  /* The next three methods are not used, but must 
     be null-implemented because they are defined  
     by MouseListener. */ 
  
  // Handle mouse entered.  
  public void mouseEntered(MouseEvent me) {  
  }  
  
  // Handle mouse exited.  
  public void mouseExited(MouseEvent me) {  
  }  
 
  // Handle mouse click.  
  public void mouseClicked(MouseEvent me) {  
  }  
  
  // Handle button pressed.  
  public void mousePressed(MouseEvent me) {  
    // save coordinates  
    oldX = me.getX();  
    oldY = me.getY();  
    draw = true; 
  }  
  
  // Handle button released.  
  public void mouseReleased(MouseEvent me) {  
    draw = false; 
  }  
  
  // Handle mouse dragged.  
  public void mouseDragged(MouseEvent me) {  
    // save coordinates  
    curX = me.getX();  
    curY = me.getY();  
    repaint();  
  }  
  
  // Handle mouse moved.  
  public void mouseMoved(MouseEvent me) {  
    // show status  
    showStatus("Moving mouse at " + me.getX() + ", " + me.getY());  
  }  
  
  // Display line in applet window. 
  public void paint(Graphics g) {  
    if(draw) 
     g.drawLine(oldX, oldY, curX, curY); 
  }  
}