TweetFollow Us on Twitter

Blinking Letters 2
Volume Number:12
Issue Number:9
Column Tag:Getting Started

The Peter Lewis Applet, After

By Dave Mark

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

Last month, we went through the first version of my color blinking text applet. As I told you then, I showed the applet to Peter Lewis (he of Anarchie and other cool Internet software fame) and he rewrote it. This month, we’ll take a look at Peter’s rewrite. As you read through Peter’s code, bear this in mind. This applet definitely is not the only way to do things. Far more importantly, this version of CWBlink introduces a number of important Java topics, all of which you should learn about and eventually master. We’ll aim to cover each topic in more detail in the coming months. For now, just enjoy.

The New CWBlink Project

The new version of CWBlink extends last month’s example with a pushbutton that adds the ability to turn blinking on and off, and also offers a convenient, well-defined place to drop into your debugger. Figure 1 shows CWBlink with color blinking turned on.

The new CWBlink project is based on two Java source files instead of one. The first file, CWBlink.java, contains the heart of the applet, and is divided into two classes. The class CWBlink extends java.applet.Applet, and is the applet itself. The class BlinkingText extends the Canvas class (a generic drawing component class), implements the Runnable interface (which means it can be a thread - see last month’s column), and defines a generic blinking text object. The CWBlink class creates and starts the BlinkingText object.

The second file, AppletFrame.java, is needed only if you want your applet to run standalone, replacing the applet frame with your own frame. This source file is definitely worth understanding. We’ll start off by listing both source code files (along with the associated HTML file), then cover the highlights of each file.

Figure 1. The CWBlink applet with color blinking turned on

If you like the experience of creating your project from scratch (as I do), launch CodeWarrior, create a new project using the Java Applet stationery, then create three new source code files. Here’s the source code for CWBlink.java:

package com.metrowerks.example.CWBlink;

import java.awt.*;

public class CWBlink extends java.applet.Applet
{
 private Button blinkButton;
 private BlinkingText blinkText;

 public String getParameter(String name)
 {
 String result = null;
 
 try
 {
 result = super.getParameter(name);
 }
 catch ( Exception e )
 {
 result = null;
 }
 
 return result;
 }

 public void init()
 {
 Panel tempPanel;
 
 String att = getParameter("speed");
 int speed = (att == null) ?
 500 : (1000 / Integer.valueOf(att).intValue());
 
 setLayout( new BorderLayout() );

 att = getParameter("blinker");
 String blinkString = (att == null) ?
 "CodeWarrior!!!" : att;
 
 blinkButton = new Button( "Blink" );
 
 tempPanel = new Panel();
 tempPanel.add( blinkButton );
 this.add( "North", tempPanel );
 
 blinkText = new BlinkingText( blinkString, speed );
 
 tempPanel = new Panel();
 tempPanel.add( blinkText );
 this.add( "Center", tempPanel );
 
 resize( 570, 170 );
 }
 
 public void start()
 {
 blinkText.start();
 }
 
 public void stop()
 {
 blinkText.stop();
 }
 
 public boolean action(Event evt, Object arg)
 {
 if ( "Blink".equals(arg) )
 {
 blinkText.ToggleBlinking();
 }
 return true;
 }
 
 public static void main(String args[])
 {
 com.metrowerks.AppletFrame.startApplet(
 "com.metrowerks.example.CWBlink.CWBlink",
 "Blink", args);
 }
}


class BlinkingText extends Canvas implements Runnable
{
 private Thread blinkThread = null;
 private String blinkString;
 private Font font;
 private int speed;
 private boolean isBlinking = false;
 private Color[] letters;
 private boolean[] is_black;
 private int current_letter = 0;
 private int old_width, old_height;
 
 private Color RandomColor()
 {
 int red, green, blue;
 
 do {
 red = (int)(Math.random() * 256);
 } while ( red > 0x8000 );
 
 do {
 green = (int)(Math.random() * 256);
 } while ( green > 0x8000 );
 
 do {
 blue = (int)(Math.random() * 256);
 } while ( blue > 0x8000 );
 
 return new java.awt.Color( red, green, blue );
 }
 
 public BlinkingText( String blinkString, int speed )
 {
 this.blinkString = blinkString;
 this.speed = speed / blinkString.length();
 this.font = new java.awt.Font( "TimesRoman",
 Font.PLAIN, 64 );
 this.letters = new Color[blinkString.length()];
 this.is_black = new boolean[blinkString.length()];
 
 for ( int i = 0; i < letters.length; i++ )
 {
 letters[i] = RandomColor();
 is_black[i] = true;
 }
 resize( 530, 70 );
 repaint();
 }
 
 public synchronized void ToggleBlinking()
 {
 isBlinking = ! isBlinking;
 notify();
 }
 
 public synchronized void PaintLetter( int the_letter )
 {
 Rectangle b = bounds();
 int width = b.width;
 int height = b.height;
 Graphics g = getGraphics();
 
 if ( old_width == width && old_height == height )
 {
 int x = 0;
 int y = height;

 g.setFont(font);
 FontMetrics fm = g.getFontMetrics();
 
 for (int index=0; index<the_letter; index++ )
 {
 int w = fm.charWidth(blinkString.charAt(index));
 x += w;
 }
 
 int w = fm.charWidth(blinkString.charAt(the_letter));
 g.setColor( isBlinking ? 
 letters[the_letter] : Color.black );
 g.clearRect( x, 0, w, height );
 g.drawString( blinkString.substring( 
 the_letter,the_letter+1), x, y );

 is_black[the_letter] = !isBlinking;
 }
 else
 {
 paint( g );
 }
 }
 
 public synchronized void paint(Graphics g)
 {
 Rectangle b = bounds();
 int width = b.width;
 int height = b.height;
 old_width = width;
 old_height = height;
 int x = 0;
 int y = height;

 g.setColor(Color.black);
 g.setFont(font);
 FontMetrics fm = g.getFontMetrics();
 
 g.clearRect( 0, 0, width, height );
 if ( isBlinking )
 {
 for (int index=0; index<blinkString.length();
 index++ )
 {
 int w = fm.charWidth(blinkString.charAt(index));
 
 g.setColor( letters[index] );
 
 g.drawString(
 blinkString.substring(index,index+1), x, y);
 x += w;
 }
 }
 else
 {
 g.drawString(blinkString, x, y );
 }
 
 for ( int index=0; index<blinkString.length(); index++ )
 {
 is_black[index] = !isBlinking;
 }
 }

 public void start()
 {
 stop();
 blinkThread = new Thread(this);
 blinkThread.start();
 }
 
 public void stop()
 {
 if ( blinkThread != null )
 {
 blinkThread.stop();
 blinkThread = null;
 }
 }
 
 public void run()
 {
 while (true)
 {
 synchronized ( this )
 {
 try
 {
 wait( 1 );
 }
 catch (Exception e)
 {
 }
 
 if ( isBlinking || !is_black[current_letter] )
 {
 if ( isBlinking )
 {
 letters[current_letter] = RandomColor();
 }
 PaintLetter( current_letter );
 }
 current_letter++;
 if ( current_letter >= blinkString.length() )
 {
 current_letter = 0;
 }
 }
 }
 }
 
 public void finalize()
 {
 stop();
 }
}

Save the source code as CWBlink.java and add it to the project. Next up, here’s the code for AppleFrame.java:

package com.metrowerks;

import java.awt.*;
import java.applet.Applet;

public class AppletFrame extends Frame
{
 public static void startApplet( String className,
 String title, String args[])
 {
 Applet a;
 Dimension appletSize;

 try {
 a = (Applet)
 Class.forName(className).newInstance();
 } catch (ClassNotFoundException e) {
 return;
 } catch (InstantiationException e) {
 return;
 } catch (IllegalAccessException e) {
 return;
 }

 a.init();
 a.start();
 
 AppletFrame f = new AppletFrame(title);
 
 f.add("Center", a);
 
 appletSize =  a.size();
 f.pack();
 f.resize(appletSize);
 f.show();
 
 }

 public AppletFrame(String name)
 {
 super(name);
 }

 public boolean handleEvent(Event e)
 {
 if (e.id == Event.WINDOW_DESTROY)
 {
 dispose();
 return true;
 }
 
 return super.handleEvent(e);
 }
}

Save this code as AppleFrame.java and add it to the project as well. OK, last file. It’s the HTML file:

<title>Blinking CodeWarrior</title>
<hr>
<applet codebase=CWBlink
 code="com/metrowerks/example/CWBlink/CWBlink.class" 
 width=530 
 height=120>
 <param name=blinker value="CodeWarrior!!!">
 <param name=speed value=2>
</applet>
<hr>
<a href="CWBlink.java">The source.</a>

Save this one as CWBlink.html and add it to the project as well. (You don’t have to add the HTML file to the project, but it does make editing the file more convenient - you just double-click on the file name in the project window.)

Once your source code and HTML files are entered and added to the project, go to the Preferences panel, Java Project pane, select Class Folder from the Project Type popup, and enter CWBlink in the Folder Name field. This will store any class files generated by this project in a folder hierarchy inside a folder named CWBlink. This option works well if you plan on serving your applet on a Web page.

Select Make from the Project menu. CodeWarrior will compile your Java code and generate the appropriate .class files. To run your applet, drag your HTML file onto the Metrowerks Java application. If you want to use the debugger, be sure the debugger is enabled and that you have the MetroNub extension installed, then drag the .class files you want to debug onto the MW Debug application. When the debugger launches, click on your source code file name in the debugger window. If your source code file is not in the same folder as the .class file, you’ll be prompted to locate the source file. This can be a hassle, so to prevent it from happening you might want to keep your source files in the same folder as your .class files, even though this is a slight pain to set up.

Once the debugger finds your source code, it lets you do all the normal pre-running things like setting breakpoints. Note that the debugger window for one class will let you set breakpoints only in the functions that belong to that class.

Try this one: Drag CWBlink.class onto the MW Debug application. In the debug window that appears, click on CWBlink.java. When the source code appears, scroll down to this function:

 public boolean action(Event evt, Object arg)
 {
 if ( "Blink".equals(arg) )
 {
 blinkText.ToggleBlinking();
 }
 return true;
 }

Set a breakpoint next to the call to blinkText.ToggleBlinking(). Now go back to the Finder and drag the HTML file onto the Metrowerks Java application. When the applet starts running, click on the Blink button. If all was set up properly, you’ll pop into the debugger at the breakpoint.

Source Code Highlights

Normally, this is where I’d step through every single line of code in the applet. But since you’ve seen a lot of this code before (last month’s column), I’ll just run through the highlights. If you don’t get something about the code, don’t worry. The important thing to take away from this month’s column is list of concepts to read up on.

Take a look at the beginning of CWBlink.java:

package com.metrowerks.example.CWBlink;

import java.awt.*;

The first thing you notice is the package statement. Packages are like C and C++ libraries. The package statement at the beginning of a Java source file gives the collection of classes in this file a name. In this case, the CWBlink and BlinkingText classes are grouped in the package com.metrowerks.example.CWBlink. It’s important that you place the .class files generated from this source file into a directory structure that matches the package name. In this case, the two files CWBlink.class and BlinkingText.class must be placed in a folder with the path com:metrowerks:example:
CWBlink. Fortunately, CodeWarrior does this for you automatically.

You’ve already seen how to access a package: use the import command. In this file, we import the java.awt package.

Note that the getParameter() code was pulled into its own method. Smart move. Gee, why didn’t I think of that?

The init() method has some important new stuff in it. First, notice the use of the Panel class. A Panel is sort of like a PowerPlant View. Java uses the concept of containers and components. A container is just like it sounds, a containing view. A component is an interface element, like a pushbutton or checkbox. A Frame is an applet’s outermost container. A Panel might contain components and other containing classes.

To simplify things, think of a Frame as a Window, and a Panel as a collection of elements you want to group together. If your applet runs in a Web browser, the outer Frame is created for you. If you plan to run the applet standalone, you’ll need to create the Frame yourself. More on that in a minute (when we discuss AppletFrame.java).

The init() method loads the speed parameter (see last month’s column), then sets a layout for the current Frame. You should read up on layouts (any Java book worth its salt will cover them), but here’s the basics.

Every container has a layout that defines how contained elements are to be arranged. For example, the BorderLayout (see java.awt.BorderLayout.html) lays out a container using members named "North", "South", "East", "West" and "Center". A component added as "North" gets placed at the top of the container. A component added as "Center" gets the space left over when the other components are laid out.

Once the init() method sets the layout, it gets the blinking text parameter, then creates a pushbutton with the text "Blink". The button is added to a panel and the panel added to the current container. Since "North" is used, the button will appear at the top of the container.

Next, a new BlinkingText object is created and added to the center of the container. Finally, the container is resized. Play with this stuff. Try using "South" or "East". Change the parameters passed to resize.

Another important CWBlink method is main(). You can actually delete this method, and remove the AppletFrame.java file from your project, if you only want to run the applet from a Web page (from within a pre-built applet Frame). If you want your applet to run standalone, though, you’ll need to build an applet Frame yourself. AppletFrame.java does this. When you are running standalone, main() will get called automatically, and the AppletFrame.startApplet() method will get called.

To learn how all this works, read through the source in AppletFrame.java. It’s not very long, and will serve as a nice introduction to Frames. Even better, you can just add the AppletFrame.java file to your own applet projects.

Finally, the BlinkingText class demonstrates the extremely important topic of threads. As you know, Java is multi-threaded. For example, there is a garbage-collecting thread that ensures that an object that is no longer referenced is deallocated, so that your Java heap won’t end up hopelessly fragmented. The Thread class is very important. Read up on it (check out java.lang.Thread.html). Think of a Thread as a separate little flow of control within your main process.

There are several ways to create a Thread. You can subclass Thread and override the necessary methods (such as run()). Alternatively, you can implement the Runnable interface, which is what BlinkingText does. Once you start a thread, the VM keeps running your threads until they all die.

The synchronized keyword marks a block of code so that only one thread can access it at a time. This means that if one thread starts executing a synchronized method, any other thread that wants to run the same method has to wait until the first method is finished. This keeps two threads from confusing each other - by messing with the same variables, for example.

Till Next Month

We intend to dig into all of these topics in detail in future columns. In the meantime, spend some time with the Java HTML docs and read a good Java book.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Dash 4.0.0 - Instant search and offline...
Dash is an API documentation browser and code snippet manager. Dash helps you store snippets of code, as well as instantly search and browse documentation for almost any API you might use (for a full... Read more
Bookends 12.7.9 - Reference management a...
Bookends is a full-featured bibliography/reference and information-management system for students and professionals. Bookends uses the cloud to sync reference libraries on all the Macs you use.... Read more
TrailRunner 3.8.834 - Route planning for...
TrailRunner is the perfect companion for runners, bikers, hikers, and all people wandering under the sky. Plan routes on a geographical map. Import GPS or workout recordings and journalize your... Read more
iFFmpeg 6.2.5 - Convert multimedia files...
iFFmpeg is a comprehensive media tool to convert movie, audio and media files between formats. The FFmpeg command line instructions can be very hard to master/understand, so iFFmpeg does all the hard... Read more
DaisyDisk 4.4 - $9.99
DaisyDisk allows you to visualize your disk usage and free up disk space by quickly finding and deleting big unused files. The program scans your disk and displays its content as a sector diagram... Read more
iFFmpeg 6.2.5 - Convert multimedia files...
iFFmpeg is a comprehensive media tool to convert movie, audio and media files between formats. The FFmpeg command line instructions can be very hard to master/understand, so iFFmpeg does all the hard... Read more
DaisyDisk 4.4 - $9.99
DaisyDisk allows you to visualize your disk usage and free up disk space by quickly finding and deleting big unused files. The program scans your disk and displays its content as a sector diagram... Read more
BetterTouchTool 2.07 - Customize Multi-T...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom... Read more
BetterTouchTool 2.071 - Customize Multi-...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom... Read more
BetterTouchTool 2.07 - Customize Multi-T...
BetterTouchTool adds many new, fully customizable gestures to the Magic Mouse, Multi-Touch MacBook trackpad, and Magic Trackpad. These gestures are customizable: Magic Mouse: Pinch in / out (zoom... Read more

Latest Forum Discussions

See All

Alto's Odyssey gets its first trail...
There's finally video evidence of Alto's Odyssey, the follow up to the 2015 App Store hit, Alto's Adventure. It looks just as soothing and atmospheric as Alto's last outing, but this time players will be journeying to the desert. Whereas Alto's... | Read more »
Last week on Pocket Gamer
What’s going on in the wider world of portable gaming? Each week we ask that question of our sister website Pocket Gamer. The PG team covers iOS gaming, just like 148Apps, but it also strays into the world of Android games and handheld consoles... | Read more »
Pokémon GO Generation 2 evolution guide
At long last, Niantic Labs finally unleashed the Generation 2 Pokémon into the wild. Pokémon GO trainers are scrambling to grab up this new set of 80 Pokémon. There are some special new tricks required to catch all of these new beasties, though.... | Read more »
The best new games we played this week
It feels as though the New Year got off to a creaking start as far as mobile games go, but that's changed over the past few weeks. The last few days alone have seen the debut of a number of wonderful games, so we thought we'd take the time to... | Read more »
Recruit more scallywags and discover new...
Get ready to show off your sea legs all over again in Oceans & Empires’ new grand update, which aims to make the act of rising to the role of seven seas ruler even more fresh and appealing, thanks to a richness of new content on both iOS and... | Read more »
Mage the Ascension: Refuge (Games)
Mage the Ascension: Refuge 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: The groundbreaking roleplaying game Mage: The Ascension manifests in our turbulent present with Refuge, an... | Read more »
Vampire: Prelude (Games)
Vampire: Prelude 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: The classic roleplaying game Vampire: The Masquerade returns to digital games with a Prelude of things to come. Experience a... | Read more »
Digby Forever Guide: How to dig to the d...
Digby Forever is a sparkling homage to arcade classics, and while you may be tiring of the number of arcade games being thrown at you, this endless digger finds many ways to stand out from the rest of the pack. The game manages to be challenging... | Read more »
The best sales on the App Store this wee...
It's been quite the week in mobile games, but if the latest releases(there were some pretty darn good ones, in case you missed out) aren't really doing the trick, perhaps some of these discounted games will. Many of these premium games had their... | Read more »
Why the new Fire Emblem Heroes update sh...
It’s exciting to see Nintendo delving into the mobile sphere, regardless of whether it’s to give fans another platform to enjoy their fans or simply a sound business venture. Two of the company's announced mobile games have finally come to... | Read more »

Price Scanner via MacPrices.net

13-inch 2.0GHz Space Gray MacBook Pro on sale...
Adorama has the non-Touch Bar 13″ 2.0GHz Space Gray MacBook Pro in stock today for $100 off MSRP. Shipping is free, and Adorama charges NY & NJ sales tax only: - 13″ 2.0GHz MacBook Pro Space Gray... Read more
13-inch Touch Bar MacBook Pros on sale for $1...
B&H Photo has select 2016 Apple 13″ Touch Bar MacBook Pros in stock today and up to $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.9GHz/512GB Touch Bar MacBook... Read more
KSI-1802R SX Disinfect-able Keyboard With Wav...
KSI has unveiled a new, innovative medical keyboard, the KSI-1802R SX, at HIMSS 2017, running February 19-22 in Orlando, Florida. KSI-1802R SX is the only keyboard that combines dual factor... Read more
15-inch Touch Bar MacBook Pros on sale for up...
Amazon has 15″ Touch Bar MacBook Pros in stock today and on sale for up to $150 off MSRP including free shipping: - 15″ 2.7GHz Touch Bar MacBook Pro Space Gray: $2720.38 $79 off MSRP - 15″ 2.7GHz... Read more
Apple’s Education discount saves up to $300 o...
Purchase a new Mac or iPad using Apple’s Education Store and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free: -... Read more
13-inch 1.6GHz/256GB MacBook Air on sale for...
Newegg has the 13″ 1.6GHz/256GB MacBook Air (MMGG2LL/A) on sale for $1029.99 including free shipping. Their price is $170 off MSRP, and it’s the lowest price available for this model. Choose Newegg... Read more
Save up to $600 with Apple refurbished Mac Pr...
Apple has Certified Refurbished Mac Pros available for up to $600 off the cost of new models. An Apple one-year warranty is included with each Mac Pro, and shipping is free. The following... Read more
12-inch 1.1GHz Retina MacBooks on sale for $1...
B&H has 12″ 1.1GHz Retina MacBooks on sale for $150 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 12″ 1.1GHz Space Gray Retina MacBook: $1149 $150 off MSRP - 12″ 1.1GHz... Read more
InTouch Health Expands iOS And Windows Produc...
Specialty telehealth enterprise provider InTouch Health has announced an expanded range of FDA Class I listed medical devices and software solutions for ambulatory, non-acute and non-emergent... Read more
iMobie Airs World’s 1st iCloud Manager with M...
iMobie Inc., an Apple-related software company, announced their newly-updated iPhone manager AnyTrans with exclusive feature to sync and manage contents across multiple iCloud accounts. With it,... Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Manager *Apple* Systems Administration - Pu...
Req ID 3315BR Position Title Manager, Apple Systems Administration Job Description The Manager of Apple Systems Administration oversees the administration and Read more
*Apple* Technician - nfrastructure (United S...
Let’s Work Together Apple Technician This position is based in Portland, ME Life at nfrastructure At nfrastructure, we understand that our success results from our Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Manager *Apple* Systems Administration - Pu...
Req ID 3315BR Position Title Manager, Apple Systems Administration Job Description The Manager of Apple Systems Administration oversees the administration and Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.