chapter15.java

// A minimal AWT-based applet.

import java.awt.*;
import java.applet.*;
/*
<applet code="SimpleApplet" width=200 height=60>
</applet>
*/

public class SimpleApplet extends Applet {
  public void paint(Graphics g) {
    g.drawString("Java makes applets easy.", 20, 20);
  }
}

// -----------------------------------------

// An AWT-based Applet skeleton.
import java.awt.*;
import java.applet.*;
/*
<applet code="AppletSkel" width=300 height=100>
</applet>
*/

public class AppletSkel extends Applet {
  // Called first.
  public void init() {
    // initialization
  }

  /* Called second, after init(). Also called whenever
     the applet is restarted. */
  public void start() {
    // start or resume execution
  }

  // Called when the applet is stopped.
  public void stop() {
    // suspends execution
  }

  /* Called when applet is terminated. This is the last
     method executed. */
  public void destroy() {
    // perform shutdown activities
  }

  // Called when an AWT-based applet's window must be restored.
  public void paint(Graphics g) {
    // redisplay contents of window
  }
}

// -----------------------------------------

/*
   Try This 15-1

   A simple banner applet.

   This applet creates a thread that scrolls
   the message contained in msg right to left
   across the applet's window.
*/
import java.awt.*;
import java.applet.*;
/*
<applet code="Banner" width=300 height=50>
</applet>
*/

public class Banner extends Applet implements Runnable {
  String msg = " Java Rules the Web ";
  Thread t;
  boolean stopFlag;

  // Initialize t to null.
  public void init() {
    t = null;
  }

  // Start thread when the applet is needed.
  public void start() {
    t = new Thread(this);
    stopFlag = false;
    t.start();
  }

  // Entry point for the thread that runs the banner.
  public void run() {
    // Request a repaint every quarter second.
    for( ; ; ) {
      try {
        repaint();
        Thread.sleep(250);
        if(stopFlag) break;
      } catch(InterruptedException exc) {}
    }
  }

  // Pause the banner.
  public void stop() {
    stopFlag = true;
    t = null;
  }

  // Display the banner.
  public void paint(Graphics g) {
    char ch;

    ch = msg.charAt(0);
    msg = msg.substring(1, msg.length());
    msg += ch;

    g.drawString(msg, 50, 30);
  }
}

// -----------------------------------------

// Using the Status Window.
import java.awt.*;
import java.applet.*;
/*
<applet code="StatusWindow" width=300 height=50>
</applet>
*/

public class StatusWindow extends Applet{
  // Display msg in applet window.
  public void paint(Graphics g) {
    g.drawString("This is in the applet window.", 10, 20);
    showStatus("This is shown in the status window.");
  }
}

// -----------------------------------------

// Pass a parameter to an applet.
import java.awt.*;
import java.applet.*;

/*
<applet code="Param" width=300 height=80>
<param name=author value="Herb and Dale">
<param name=purpose value="Demonstrate Parameters">
<param name=version value=2>
</applet>
*/

public class Param extends Applet {
  String author;
  String purpose;
  int ver;

  public void start() {
    String temp;

    author = getParameter("author");
    if(author == null) author = "not found";

    purpose = getParameter("purpose");
    if(purpose == null) purpose = "not found";

    temp = getParameter("version");
    try {
      if(temp != null)
        ver = Integer.parseInt(temp);
      else
        ver = 0;
    } catch(NumberFormatException exc) {
        ver = -1; // error code
    }
  }

  public void paint(Graphics g) {
    g.drawString("Purpose: " + purpose, 10, 20);
    g.drawString("By: " + author, 10, 40);
    g.drawString("Version: " + ver, 10, 60);
  }
}

// -----------------------------------------

class MyClass {
  int a;
  int b;

  // Initialize a and b individually.
  MyClass(int i, int j) {
    a = i;
    b = j;
  }

  // Use this() to initialize a and b to the same value.
  MyClass(int i) {
    this(i, i); // invokes MyClass(i, i)
  }
}