TweetFollow Us on Twitter

Blinking Letters
Volume Number:12
Issue Number:8
Column Tag:Getting Started

Blinking Letters, Before

By Dave Mark

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

I just got back from the World Wide Developer’s Conference, where I got very little sleep but had a fantastic time. I saw Gil Amelio’s long-awaited speech, reunited with friends I only get to see a few times a year, got a chance to hone my Java skills, smoked some cigars, and even took a small side trip to Napa Valley.

Before I got to the show, I wrote a small applet for this month’s column. All puffed up with pride, I showed the applet to Peter Lewis (if you don’t know Peter, check out Anarchie, along with his other cool Internet shareware, and peruse the May 1996 issue of MacTech™ Magazine, in which he features heavily), and asked him if he had any comments. What I got back from Peter was a complete rewrite that had a better design, and ran a lot faster to boot!

So here’s what I’m going to do. This month, we’ll go over my original applet, step by step. Once you understand the applet, take some time to think about how you might improve the design. Next month, we’ll take a look at Peter Lewis’ rewrite.

The Original Applet

My applet started life as one of the standard sample Java applets that ships with the JDK. The original Blink was written by Arthur van Hoff (thanks, Arthur) and is shown in Figure 1. It paints a specified string in the applet window, then repeatedly and randomly redraws the words in the window in a series of related colors. (Some words are drawn in the background color, rendering them invisible.)

Figure 1. The original Blink,
as found in the Sun Java sample applets

I rewrote Blink so that it would display its string in a bigger font, blinking the individual letters in completely random colors, as opposed to the related colors used by original Blink. Since I used CodeWarrior to build the applet, I renamed it CWBlink.

Figure 2. My rewrite of Blink, now called CWBlink

Creating the CWBlink Applet

Here’s how I created the CWBlink applet. I started in the CodeWarrior IDE. Since CodeWarrior uses a front-end/back-end architecture (front-end drop-ins for language, back-end drop-ins for target machines), they use the same IDE and debugger for Java as they use for C, C++, and Pascal.

Inside the IDE, I created a new project, using the Java Applet stationery (Figure 3).

Figure 3. The New Project dialog box,
showing the Java Applet stationery

Figure 4. The new Java Applet project window,
before we replace the .html and .java files

Once the project was created (Figure 4), the next step was to replace the .html and .java files with our own. First, I double-clicked the file <replace me Applet>.html in the Project window. When the stationery file opens (notice that it is marked as read-only), I selected Save As... from the File menu and saved the file as CWBlink.html. Next, I replaced the text in the .html file with the following:

<title>Blinking CodeWarrior</title>
<hr>
<applet codebase="CWBlink Classes" code="CWBlink.class" width=530 height=100>
<param name=blinker value="CodeWarrior!!!">
<param name=speed value=1000>
</applet>
<hr>
<a href="CWBlink.java">The source.</a>

Once your HTML is typed in, save the code and close the file.

The HTML code should look familiar. Note that the codebase attribute tells the Java virtual machine the name of the folder containing your class files. The code attribute tells the VM the name of the class file to start with. The blinker parameter is the string that does the blinking. The speed parameter lets you change the speed of the blinking.

Next, double-click the file <replace me Applet>.java. Save the file as CWBlink.java. Replace the contents of the file with the following:

import java.awt.*;

public class CWBlink extends java.applet.Applet
 implements Runnable
{
 Thread blinkThread;
 String blinkString;
 Font   font;
 int    speed;

 public void init()
 {
 font = new java.awt.Font(
 "TimesRoman", Font.PLAIN, 64);
 
 String att = getParameter("speed");
 speed = (att == null) ? 400 :
 (1000 / Integer.valueOf(att).intValue());
 
 att = getParameter("blinker");
 blinkString = (att == null) ? "CodeWarrior!!!" : att;
 }
  
 public void paint(Graphics g)
 {
 int x = 0, y = font.getSize()-10;

 g.setColor(Color.black);
 g.setFont(font);
 FontMetrics fm = g.getFontMetrics();
 
 for (int index=0; index<blinkString.length(); index++ )
 {
 int red = (int)(Math.random() * 256);
 int green = (int)(Math.random() * 256);
 int blue = (int)(Math.random() * 256);
 
 char character = blinkString.charAt(index);
 int w = fm.charWidth(character);
   
 g.setColor( new java.awt.Color( red, green, blue ) );
 
 Character c = new Character( character );
 g.drawString(c.toString(), x, y );
 x += w;
 }
 }

 public void start()
 {
 blinkThread = new Thread(this);
 blinkThread.start();
 }

 public void stop()
 {
 blinkThread.stop();
 }

 public void run()
 {
 while (true)
 {
 try {Thread.currentThread().sleep(speed);}
 catch (InterruptedException e){}
 repaint();
 }
 }
}

The last step in setting up your project is to tell CodeWarrior how you want your applet classes saved. Select Preferences from the Edit menu. When the Preferences dialog appears (Figure 5), select the Java Project item under the Project heading. Make sure “Class Folder” is selected from the Project Type popup. Now type CWBlink Classes in the Folder Name field. This tells CodeWarrior to save all of your classes as .class files in a folder named CWBlink Classes, which is what’s expected by the HTML you typed in earlier.

Figure 5. The Java Project pane from
CodeWarrior’s Preferences dialog

Select Make from the Project menu to compile your .java file and save out your new .class file. Once your code compiles, CodeWarrior will create a new folder called CWBlink Classes, then create a new class file named CWBlink.class inside the CWBlink Classes folder. Once that happens, drag your HTML file onto the Metrowerks Java application. Metrowerks Java will parse your HTML code and run your brand new blinking applet.

Let’s take a look at the source code.

CWBlink Source Code

CWBlink.java starts by importing the java.awt classes. Next, the CWBlink class is defined. Notice that CWBlink extends the Applet class (you’ve seen this before) and also implements the Runnable interface (something new). Here’s what the Sun HTML doc has to say about the java.lang.Runnable interface:

“This interface is designed to provide a common protocol for Objects that wish to execute code while they are active. For example, Runnable is implemented by class Thread. Being active simply means that a thread has been started and has not yet been stopped.

“In addition, Runnable provides the means for a class to be active while not subclassing Thread. A class that implements Runnable can run without subclassing Thread by instantiating a Thread instance and passing itself in as the target. In most cases, the Runnable interface should be used if you are only planning to override the run() method and no other Thread methods. This is important because classes should not be subclassed unless the programmer intends on modifying or enhancing the fundamental behavior of the class.”

Basically, extending an existing class is the traditional subclassing mechanism you are used to from C++. An interface defines a set of methods and variables that will be available from within any class implementing that interface. For example, to implement the Runnable interface, you must provide a method named run() that gets executed when your object is activated. As the HTML summary indicates, the Runnable interface is implemented by the Thread class. The run() method is where the thread’s action takes place.

import java.awt.*;

public class CWBlink extends java.applet.Applet
 implements Runnable
{
 Thread blinkThread;
 String blinkString;
 Font   font;
 int    speed;

The init() method is called when the applet is created. We’ll start off the initialization process by creating a Font object that defines how the blinking text will appear. Next, we’ll load the speed and blinker parameters. Note that speed gets a default value of 400 (otherwise, the value is 1000 divided by the provided value) and blinkString gets a default value of "CodeWarrior!!!".

 public void init()
 {
 font = new java.awt.Font(
 "TimesRoman", Font.PLAIN, 64);
 
 String att = getParameter("speed");
 speed = (att == null) ? 400 :
 (1000 / Integer.valueOf(att).intValue());
 
 att = getParameter("blinker");
 blinkString = (att == null) ? "CodeWarrior!!!" : att;
 }

paint() gets called when the applet’s pane gets an update event. We’ll draw the blinkString at the x and y coordinates. We use the font’s point size to calculate the point where we draw the string in the applet’s pane.

 public void paint(Graphics g)
 {
 int x = 0, y = font.getSize()-10;

We’ll set the foreground color to black and the current font to font. We’ll also build a FontMetrics object from the current Graphics environment. To learn about FontMetrics, see the HTML file java.awt.FontMetrics. This will give us access to methods like charWidth() which lets us calculate the proper x-coordinate for the next letter to be drawn, based on the width of the current character.

 g.setColor(Color.black);
 g.setFont(font);
 FontMetrics fm = g.getFontMetrics();

Next, we’ll step through the blinkString, one letter at a time. For each letter, we’ll calculate a random value for red, green, and blue. We’ll store the current character in character, then calculate the character’s width.

 for (int index=0; index<blinkString.length(); index++ )
 {
 int red = (int)(Math.random() * 256);
 int green = (int)(Math.random() * 256);
 int blue = (int)(Math.random() * 256);
 
 char character = blinkString.charAt(index);
 int w = fm.charWidth(character);

We’ll set the current color using our random red, green, and blue values. Next, we’ll create a new Character object (note that Character is different from char - see java.lang.Character), which gives us an easy way to convert a single character to a string. We need a string to pass to drawString(), and the Character wrapper gives us an easy way to get there. If anyone out there can think of a simpler way to draw the character on the screen at the specified x and y location, please let me know. Just be sure you test your theory before you write!

Once we draw the character, we’ll bump x by the width of the character.

 g.setColor( new java.awt.Color( red, green, blue ) );
 
 Character c = new Character( character );
 g.drawString(c.toString(), x, y );
 x += w;
 }
 }

start() is similar to init(), but gets called when the applet’s document is visited. We’ll create a new Thread object and call its start() method. When the applet’s document is no longer on the screen, the stop() method is called. In our case, we’ll call the Thread’s stop() method to stop the thread.

 public void start()
 {
 blinkThread = new Thread(this);
 blinkThread.start();
 }

 public void stop()
 {
 blinkThread.stop();
 }

Remember that the run() method contains the body of the thread we are starting up. Our thread enters an infinite loop. The loop tries a sleep() for speed milliseconds. We catch the InterruptedException exception (which occurs when another Thread interrupts this thread), but we do nothing about it. The loop ends by forcing a repaint of the applet.

 public void run()
 {
 while (true)
 {
 try {Thread.currentThread().sleep(speed);}
 catch (InterruptedException e){}
 repaint();
 }
 }
}

Till Next Month...

This month’s applet introduced the concept of FontMetrics, type wrappers (in our case, java.lang.Character), and Threads, along with a quick tour of CodeWarrior’s Java environment. Next month, we’ll take a look at Peter Lewis’ rewrite of this applet. Think about how you might improve the design of this applet. What changes would you make? Peter’s changes were very interesting and definitely worth exploring. See you next month.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Skype 8.52.0.138 - Voice-over-internet p...
Skype allows you to talk to friends, family and co-workers across the Internet without the inconvenience of long distance telephone charges. Using peer-to-peer data transmission technology, Skype... Read more
Bookends 13.2.6 - 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
BusyContacts 1.4.0 - Fast, efficient con...
BusyContacts is a contact manager for OS X that makes creating, finding, and managing contacts faster and more efficient. It brings to contact management the same power, flexibility, and sharing... Read more
Chromium 77.0.3865.75 - Fast and stable...
Chromium is an open-source browser project that aims to build a safer, faster, and more stable way for all Internet users to experience the web. Version 77.0.3865.75: A list of changes is available... Read more
DiskCatalogMaker 7.5.5 - Catalog your di...
DiskCatalogMaker is a simple disk management tool which catalogs disks. Simple, light-weight, and fast Finder-like intuitive look and feel Super-fast search algorithm Can compress catalog data for... Read more
Alfred 4.0.4 - Quick launcher for apps a...
Alfred is an award-winning productivity application for OS X. Alfred saves you time when you search for files online or on your Mac. Be more productive with hotkeys, keywords, and file actions at... Read more
A Better Finder Rename 10.45 - File, pho...
A Better Finder Rename is the most complete renaming solution available on the market today. That's why, since 1996, tens of thousands of hobbyists, professionals and businesses depend on A Better... Read more
iFinance 4.5.11 - Comprehensively manage...
iFinance allows you to keep track of your income and spending -- from your lunchbreak coffee to your new car -- in the most convenient and fastest way. Clearly arranged transaction lists of all your... Read more
OmniGraffle Pro 7.11.3 - Create diagrams...
OmniGraffle Pro helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use... Read more
BBEdit 12.6.7 - Powerful text and HTML e...
BBEdit is the leading professional HTML and text editor for the Mac. Specifically crafted in response to the needs of Web authors and software developers, this award-winning product provides a... Read more

Latest Forum Discussions

See All

Five Nights at Freddy's AR: Special...
Five Nights at Freddy's AR: Special Delivery is a terrifying new nightmare from developer Illumix. Last week, FNAF fans were sent into a frenzy by a short teaser for what we now know to be Special Delivery. Those in the comments were quick to... | Read more »
Rush Rally 3's new live events are...
Last week, Rush Rally 3 got updated with live events, and it’s one of the best things to happen to racing games on mobile. Prior to this update, the game already had multiplayer, but live events are more convenient in the sense that it’s somewhat... | Read more »
Why your free-to-play racer sucks
It’s been this way for a while now, but playing Hot Wheels Infinite Loop really highlights a big issue with free-to-play mobile racing games: They suck. It doesn’t matter if you’re trying going for realism, cart racing, or arcade nonsense, they’re... | Read more »
Steam Link Spotlight - The Banner Saga 3
Steam Link Spotlight is a new feature where we take a look at PC games that play exceptionally well using the Steam Link app. Our last entry talked about Terry Cavanaugh’s incredible Dicey Dungeons. Read about how it’s a great mobile experience... | Read more »
PSA: GRIS has some issues
You may or may not have seen that Devolver Digital just released GRIS on the App Store, but we wanted to do a quick public service announcement to say that you might not want to hop on buying it just yet. The puzzle platformer has come to small... | Read more »
Explore the world around you in new matc...
Got a hankering for a fresh-feeling Match-3 puzzle game that offers a unique twist? You might find exactly what you’re looking for with What a Wonderful World, a new spin on the classic mobile genre which merges entertaining puzzles with global... | Read more »
Combo Quest (Games)
Combo Quest 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: Combo Quest is an epic, time tap role-playing adventure. In this unique masterpiece, you are a knight on a heroic quest to retrieve... | Read more »
Hero Emblems (Games)
Hero Emblems 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: ** 25% OFF for a limited time to celebrate the release ** ** Note for iPhone 6 user: If it doesn't run fullscreen on your device... | Read more »
Puzzle Blitz (Games)
Puzzle Blitz 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Puzzle Blitz is a frantic puzzle solving race against the clock! Solve as many puzzles as you can, before time runs out! You have... | Read more »
Sky Patrol (Games)
Sky Patrol 1.0.1 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0.1 (iTunes) Description: 'Strategic Twist On The Classic Shooter Genre' - Indie Game Mag... | Read more »

Price Scanner via MacPrices.net

Save $150-$250 on 10.2″ WiFi + Cellular iPads...
Verizon is offering $150-$250 discounts on Apple’s new 10.2″ WiFi + Cellular iPad with service. Buy the iPad itself and save $150. Save $250 on the purchase of an iPad along with an iPhone. The fine... Read more
Apple continues to offer 13″ 2.3GHz Dual-Core...
Apple has Certified Refurbished 2017 13″ 2.3GHz Dual-Core non-Touch Bar MacBook Pros available starting at $1019. An standard Apple one-year warranty is included with each model, outer cases are new... Read more
Apple restocks 2018 MacBook Airs, Certified R...
Apple has restocked Certified Refurbished 2018 13″ MacBook Airs starting at only $849. Each MacBook features a new outer case, comes with a standard Apple one-year warranty, and is shipped free. The... Read more
Sunday Sale! 2019 27″ 5K 6-Core iMacs for $20...
B&H Photo has the new 2019 27″ 5K 6-Core iMacs on stock today and on sale for up to $250 off Apple’s MSRP. Overnight shipping is free to many locations in the US. These are the same iMacs sold by... Read more
Weekend Sale! 2019 13″ MacBook Airs for $200...
Amazon has new 2019 13″ MacBook Airs on sale for $200 off Apple’s MSRP, with prices starting at $899, each including free shipping. Be sure to select Amazon as the seller during checkout, rather than... Read more
2019 15″ MacBook Pros now on sale for $350-$4...
B&H Photo has Apple’s 2019 15″ 6-Core and 8-Core MacBook Pros on sale today for $350-$400 off MSRP, starting at $2049, with free overnight shipping available to many addresses in the US: – 2019... Read more
Buy one Apple Watch Series 5 at Verizon, get...
Buy one Apple Watch Series 5 at Verizon, and get a second Watch for 50% off. Plus save $10 on your first month of service. The fine print: “Buy Apple Watch, get another up to 50% off on us. Plus $10... Read more
Sprint offers 64GB iPhone 11 for free to new...
Sprint will include the 64GB iPhone 11 for free for new customers with an eligible trade-in in of the iPhone 7 or newer through September 19, 2019. The fine print: “iPhone 11 64GB $0/mo. iPhone 11... Read more
Verizon offers new iPhone 11 models for up to...
Verizon is offering Apple’s new iPhone 11 models for $500 off MSRP to new customers with an eligible trade-in (see list below). Discount is applied via monthly bill credits over 24 months. Verizon is... Read more
AT&T offers free $300 reward card + free...
AT&T Wireless will include a second free 64GB iPhone 11 with the purchase of one eligible iPhone at full price. They will also include a free $300 rewards card. The fine print: “Buy an elig.... Read more

Jobs Board

Student Employment (Blue *Apple* Cafe) Spri...
Student Employment (Blue Apple Cafe) Spring 2019 Penn State University Campus/Location: Penn State Brandywine Campus City: Media, PA Date Announced: 12/20/2018 Date Read more
Best Buy *Apple* Computing Master - Best Bu...
**732359BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Store Associates **Location Number:** 000171-Winchester Road-Store **Job Description:** Read more
*Apple* Mobile Master - Best Buy (United Sta...
**732324BR** **Job Title:** Apple Mobile Master **Job Category:** Store Associates **Location Number:** 000013-Fargo-Store **Job Description:** **What does a Best Read more
Best Buy *Apple* Computing Master - Best Bu...
**732455BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Sales **Location Number:** 000449-Auburn Hills-Store **Job Description:** **What does a Read more
*Apple* Mobility Pro - Best Buy (United Stat...
**732490BR** **Job Title:** Apple Mobility Pro **Job Category:** Store Associates **Location Number:** 000449-Auburn Hills-Store **Job Description:** At Best Buy, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.