TweetFollow Us on Twitter

Java Events
Volume Number:12
Issue Number:12
Column Tag:Getting Started

Java Events

By Dave Mark

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

Originally I was planning to cover double-buffering in this month’s column. I started writing a cool banner animator, then I got a little side-tracked playing with Java’s event-handling mechanism. As I explored (and as my animation applet took on a life of its own!), I realized that we never really covered events. Since events are the heart and soul of your applet’s user interaction, and since I ended up writing this nifty little event doodad anyway, I thought we would dive into events now and put off animation for the moment.

The Ultimate Event Handler

This month’s applet is called eventHandler. For you Primer readers, eventHandler is similar to eventTracker. As you click, drag, and type, the events associated with those actions are displayed in a scrolling list. Figure 1 shows eventHandler running in the Metrowerks Java applet viewer. One thing I learned from this exercise is that no two applet viewers behave exactly the same way. For example, the Metrowerks Java viewer swallows keyUp events. In Netscape Gold 3.0 (see Figure 2), the keyUp events show up, but mouseMove events are not reported properly. The Sun JDK Applet Viewer 1.0.2 (not shown) doesn’t handle clipping correctly. <sigh>. Well, at least these applet viewers are much better than their predecessors!

Figure 1. eventHandler running in Metrowerks’ Applet Viewer. Notice that keyUp events are swallowed. See Figure 2.

Figure 2. eventHandler running in Netscape Gold 3.0. The keyUp events are there, but mouseMove events (not shown) don’t work right.

eventHandler consists of two major areas (each with its own label). On the top is a Canvas with a yellow background. All the events trapped by this Canvas are listed in the scrolling TextArea on the bottom. When the keyboard focus is on the Canvas, its border is drawn in red. When the Canvas loses the keyboard focus, the border is redrawn as yellow.

If you click or drag in the Canvas, the appropriate events get listed in the scrolling list. If you type while the focus is in the Canvas, the actual key names are listed when the keyDown event is reported. Note that I don’t report the mouseMove event, which is supposed to occur when you move the mouse. Unfortunately, the Metrowerks viewer is the only one that handles this correctly. Both Netscape and the Sun viewer report a steady stream of mouseMove events, even when the mouse is perfectly still! This can be a real pain, since any other events tend to get swept away in a flood of incorrectly reported mouseMove events. Add a mouseMove handler to the code below, just to see this for yourself.

The eventHandler Source Code

Create a new project using the Java Applet stationery. Create a source code file named eventHandler.java and add it to the project. Here’s the source code:

import java.awt.*;

public class eventCanvas extends Canvas
{
 booleanhasFocus;
 
 eventCanvas( int width, int height )
 {
 setBackground( Color.yellow );
 resize( width, height );
 
 hasFocus = false;
 }
 
 public boolean mouseUp( Event e, int x, int y )
 {
 eventHandler.reportEvent( “mouseUp” );
 return true;
 }
 
 public boolean mouseDown( Event e, int x, int y )
 {
 eventHandler.reportEvent( “mouseDown” );
 return true;
 }
 
 public boolean mouseDrag( Event e, int x, int y )
 {
 eventHandler.reportEvent( “mouseDrag” );
 return true;
 }
 
 public boolean mouseEnter( Event e, int x, int y )
 {
 eventHandler.reportEvent( “mouseEnter” );
 return true;
 }
 
 public boolean mouseExit( Event e, int x, int y )
 {
 eventHandler.reportEvent( “mouseExit” );
 return true;
 }
 
 public boolean keyDown( Event e, int key )
 {
 String eventString = “keyDown: “;
 String keyName, modifierName;
 
 modifierName = getModifierName( e );
 if ( modifierName != null )
 eventString += modifierName;
 
 keyName = getKeyName( key );
 
 if ( keyName != null )
 eventString += keyName;
 else if (( key >= 32 ) && ( key <= 127 ))
 eventString += new Character( (char)key ).toString();
 else
 eventString += key;
 
 eventHandler.reportEvent( eventString );
 
 return true;
 }
 
 public String getModifierName( Event e )
 {
 if ( e.controlDown() )
 return( “Control-” );
 if ( e.metaDown() )
 return( “Meta-” );
 if ( e.shiftDown() )
 return( “Shift-” );
 
 return null;
 }
 
 public String getKeyName( int key )
 {
 switch ( key )
 {
 case Event.F1: return “F1”;
 case Event.F2: return “F2”;
 case Event.F3: return “F3”;
 case Event.F4: return “F4”;
 case Event.F5: return “F5”;
 case Event.F6: return “F6”;
 case Event.F7: return “F7”;
 case Event.F8: return “F8”;
 case Event.F9: return “F9”;
 case Event.F10: return “F10”;
 case Event.F11: return “F11”;
 case Event.F12: return “F12”;
 case Event.HOME: return “HOME”;
 case Event.END: return “END”;
 case Event.LEFT: return “Left Arrow”;
 case Event.RIGHT: return “Right Arrow”;
 case Event.UP: return “Up Arrow”;
 case Event.DOWN: return “DownArrow”;
 case Event.PGUP: return “Page Up”;
 case Event.PGDN: return “Page Down”;
 }
 
 return null;
 }
 
 public boolean keyUp( Event e, int key )
 {
 eventHandler.reportEvent( “keyUp” );
 
 return true;
 }
 
 public boolean gotFocus(Event e, Object what)
 {
 hasFocus = true;
 eventHandler.reportEvent( “gotFocus” );
 repaint();
 
 return true;
 }
 
 public boolean lostFocus(Event e, Object what)
 {
 hasFocus = false;
 eventHandler.reportEvent( “lostFocus” );
 repaint();
 
 return true;
 }
 
 public void paint( Graphics g )
 {
 Rectangler;
 
 r = bounds();
 g = getGraphics();
 
 if ( hasFocus )
 g.setColor( Color.red );
 else
 g.setColor( Color.yellow );
 
 g.drawRect( 0, 0, r.width-1, r.height-1 );
 g.drawRect( 1, 1, r.width-3, r.height-3 );
 }
}

public class eventHandler extends java.applet.Applet
{
 eventCanvaseCanvas;
 static TextArea tArea;
 
 public void init()
 {
 add( new Label( “Click and type in this Canvas:” ) );
 
 eCanvas = new eventCanvas( 200, 100 );
 add( eCanvas );
 
 add( new Label( “Here’s a list of canvas events:” ) );
 
 tArea = new TextArea( 10, 30 );
 add( tArea );
 }
 
 public static void reportEvent( String eventString )
 {
 tArea.appendText( eventString + “\r” );
 }
}

Now create a file named eventHandler.html and add it to the project as well. Here’s the HTML:

<title>Event Handler</title>
<hr>
<applet codebase=”eventHandler Classes” code=”eventHandler.class” width=290 
height=320>
</applet>
<hr>
<a href=”eventHandler.java”>The source.</a>

Now go into the Project Settings dialog (Under CW10, select Project Settings... from the Edit menu. See Figure 3. Earlier versions, Preferences from the Edit menu) and click on Project/Java Project. Select Class Folder from the Project Type popup and type “eventHandler Classes” as the File Name. Note that we’re no longer using non-ASCII characters (like ƒ) in our Java-specific file and folder names. Though some environments can deal with these special characters, other environments, like Netscape, don’t recognize them and won’t be able to locate your class files.

Figure 3. The CW10 Project Settings dialog.

A terrific feature introduced with CW10 (there are a bunch of them) is the Set... button in the Project Settings dialog, which lets you select the application to which your html will be sent when you select Run from the Project menu. So if you like, you can use Netscape to test your applet or, if you prefer, use the applet viewer that ships with the JDK or with CW10. No matter which applet viewer you choose, be aware of any class caching schemes used by the viewer. If the viewer caches your class, it won’t replace the class each time you run with a new version unless you quit the viewer each time you run. As I write this, I don’t know of any work-arounds for this. On the other hand, by the time you read this, maybe this won’t be an issue anymore.

Running eventHandler

Once your source is entered, build your .class file and drop your html file on your favorite viewer. If you are using CodeWarrior, select Run from the Project menu. Once your applet appears, generate some events. Try dragging the mouse within the Canvas to generate a stream of mouseDrag events. Click on the Canvas to generate a gotFocus event, then click outside the Canvas to lose the focus. Click on the Canvas to regain the focus, then bring the Finder to the front. Notice that the focus is lost, then regained when you bring the applet viewer to the front.

Experiment!

The eventHandler Source Code

eventHandler is broken into two classes. The eventCanvas class implements the yellow canvas area, adding to it the various event handlers. The hasFocus variable is a boolean that specifies whether the Canvas currently has the keyboard focus. The constructor takes a width and height, sets the background color to yellow, resizes the Canvas, and sets the focus to false.

import java.awt.*;

public class eventCanvas extends Canvas
{
 booleanhasFocus;
 
 eventCanvas( int width, int height )


 {
 setBackground( Color.yellow );
 resize( width, height );
 
 hasFocus = false;
 }

Each of the event handlers overrides a default Canvas event handler. Each one reports its event by calling the static eventHandler function reportEvent(). We will get to that when we explore the eventHandler class in a bit. Each handler returns true, signifying that it has dealt with the event. mouseUp() and mouseDown() are called when the mouse button is pressed or released within the eventCanvas component.

 public boolean mouseUp( Event e, int x, int y )
 {
 eventHandler.reportEvent( “mouseUp” );
 return true;
 }
 
 public boolean mouseDown( Event e, int x, int y )
 {
 eventHandler.reportEvent( “mouseDown” );
 return true;
 }

mouseDrag() is called when the mouse is dragged within the eventCanvas, and mouseEnter() and mouseExit() are called when the mouse enters or leaves the eventCanvas boundaries.

 public boolean mouseDrag( Event e, int x, int y )
 {
 eventHandler.reportEvent( “mouseDrag” );
 return true;
 }
 
 public boolean mouseEnter( Event e, int x, int y )
 {
 eventHandler.reportEvent( “mouseEnter” );
 return true;
 }
 
 public boolean mouseExit( Event e, int x, int y )
 {
 eventHandler.reportEvent( “mouseExit” );
 return true;
 }

keyDown() is called when a key is pressed, ONLY IF the eventCanvas has the focus. The keyDown() code basically builds a string reflecting the name of the key that was pressed. getModifierName() checks to see if the control, meta, or shift keys were down and, if so, adds the appropriate modifier name to the string. getKeyName() does a lookup on some standard Java key names. This table should be larger, but these are the only keynames I could find in the documentation. For example, I couldn’t find a TAB constant.

If the key was an ASCII between 32 and 127, the character name is used, otherwise the key number is used. keyDown() is very simple-minded. After you experiment with it a bit, you might want to add more complexity to it to handle the other key types.

 public boolean keyDown( Event e, int key )
 {
 String eventString = “keyDown: “;
 String keyName, modifierName;
 
 modifierName = getModifierName( e );
 if ( modifierName != null )
 eventString += modifierName;
 
 keyName = getKeyName( key );
 
 if ( keyName != null )
 eventString += keyName;
 else if (( key >= 32 ) && ( key <= 127 ))
 eventString += new Character( (char)key ).toString();
 else
 eventString += key;
 
 eventHandler.reportEvent( eventString );
 
 return true;
 }
 
 public String getModifierName( Event e )
 {
 if ( e.controlDown() )
 return( “Control-” );
 if ( e.metaDown() )
 return( “Meta-” );
 if ( e.shiftDown() )
 return( “Shift-” );
 
 return null;
 }
 
 public String getKeyName( int key )
 {
 switch ( key )
 {
 case Event.F1: return “F1”;
 case Event.F2: return “F2”;
 case Event.F3: return “F3”;
 case Event.F4: return “F4”;
 case Event.F5: return “F5”;
 case Event.F6: return “F6”;
 case Event.F7: return “F7”;
 case Event.F8: return “F8”;
 case Event.F9: return “F9”;
 case Event.F10: return “F10”;
 case Event.F11: return “F11”;
 case Event.F12: return “F12”;
 case Event.HOME: return “HOME”;
 case Event.END: return “END”;
 case Event.LEFT: return “Left Arrow”;
 case Event.RIGHT: return “Right Arrow”;
 case Event.UP: return “Up Arrow”;
 case Event.DOWN: return “DownArrow”;
 case Event.PGUP: return “Page Up”;
 case Event.PGDN: return “Page Down”;
 }
 
 return null;
 }
 
 public boolean keyUp( Event e, int key )
 {
 eventHandler.reportEvent( “keyUp” );
 
 return true;
 }

gotFocus() sets hasFocus to true, reports the event, and forces a redraw. lostFocus() sets hasFocus to false and does the same.

 public boolean gotFocus(Event e, Object what)
 {
 hasFocus = true;
 eventHandler.reportEvent( “gotFocus” );
 repaint();
 
 return true;
 }
 
 public boolean lostFocus(Event e, Object what)
 {
 hasFocus = false;
 eventHandler.reportEvent( “lostFocus” );
 repaint();
 
 return true;
 }

paint() sets the drawing color to red if the eventCanvas has the focus (yellow otherwise), then draws the bordering rectangle based on the bounding rectangle of the eventCanvas. Another peculiarity I ran into was trying to draw a pair of rectangles, one inside the other. I expected to use r.width-2 and r.height-2 as parameters to the second drawRect call. Somehow this didn’t produce the results I expected. I tried this with all the viewers, and got different results with each one. I’m guessing that this is a flaw in the viewer implementation, though of course that assumption is pretty dangerous! If anyone sees a bug in this code, let me know <dmark@aol.com>.

 public void paint( Graphics g )
 {
 Rectangler;
 
 r = bounds();
 g = getGraphics();
 
 if ( hasFocus )
 g.setColor( Color.red );
 else
 g.setColor( Color.yellow );
 
 g.drawRect( 0, 0, r.width-1, r.height-1 );
 g.drawRect( 1, 1, r.width-3, r.height-3 );
 }
}

The eventHandler class implements the applet itself. The reportEvent() method is static so it can be called from outside the class without having a specific eventHandle object reference. This is one way to solve this problem. There are certainly others. We could have retrieved the current applet from within the eventCanvas class, coerced that reference to an eventCanvas and used it to call reportEvent(). I think the first way is better. Any other ideas? Let me know.

The TextArea variable tArea was also made static so it could be referenced from within the static reportEvent. The disadvantage here is that this approach limits you to single occurances of the applet. Again, I’m definitely interested in hearing any other ideas you might have.

public class eventHandler extends java.applet.Applet
{
 eventCanvaseCanvas;
 static TextArea tArea;
 
 public void init()
 {
 add( new Label( “Click and type in this Canvas:” ) );
 
 eCanvas = new eventCanvas( 200, 100 );
 add( eCanvas );
 
 add( new Label( “Here’s a list of canvas events:” ) );
 
 tArea = new TextArea( 10, 30 );
 add( tArea );
 }
 
 public static void reportEvent( String eventString )
 {
 tArea.appendText( eventString + “\r” );
 }
}

Till Next Month...

This was one of the most interesting applets I’ve worked on, both because of the nature of the problem the applet solved, and because of the many differences between the various applet viewers. Java is still evolving rapidly and the tools will be playing catch-up for a while. Have a very happy holiday season and I look forward to seeing you all in 1997.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Microsoft Remote Desktop 8.0.34 - Connec...
With Microsoft Remote Desktop, you can connect to a remote PC and your work resources from almost anywhere. Experience the power of Windows with RemoteFX in a Remote Desktop client designed to help... Read more
Data Rescue 4.2.3 - Powerful hard drive...
Use Data Rescue to recover: crashed, corrupted or non-mounting hard drive deleted, damaged, or lost files reformatted or erased hard drive One powerful new feature found in Data Rescue 4 is... Read more
Viber 6.2.0 - Send messages and make cal...
Viber lets you send free messages and make free calls to other Viber users, on any device and network, in any country! Viber syncs your contacts, messages and call history with your mobile device, so... Read more
Lyn 1.7.2 - Lightweight image browser an...
Lyn is a fast, lightweight image browser and viewer designed for photographers, graphic artists, and Web designers. Featuring an extremely versatile and aesthetically pleasing interface, it delivers... Read more
Lyn 1.7.2 - Lightweight image browser an...
Lyn is a fast, lightweight image browser and viewer designed for photographers, graphic artists, and Web designers. Featuring an extremely versatile and aesthetically pleasing interface, it delivers... Read more
Tunnelblick 3.6.7beta02 - GUI for OpenVP...
Tunnelblick is a free, open source graphic user interface for OpenVPN on OS X. It provides easy control of OpenVPN client and/or server connections. It comes as a ready-to-use application with all... Read more
jAlbum Pro 13.4 - Organize your digital...
jAlbum Pro has all the features you love in jAlbum, but comes with a commercial license. You can create gorgeous custom photo galleries for the Web without writing a line of code! Beginner-friendly... Read more
calibre 2.65.1 - Complete e-book library...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital librarian... Read more
jAlbum 13.4 - Create custom photo galler...
With jAlbum, you can create gorgeous custom photo galleries for the Web without writing a line of code! Beginner-friendly, with pro results - Simply drag and drop photos into groups, choose a design... Read more
Backblaze 4.2.0.966 - Online backup serv...
Backblaze is an online backup service designed from the ground-up for the Mac. With unlimited storage available for $5 per month, as well as a free 15-day trial, peace of mind is within reach with... Read more

Mummy madness in new action game Tomb He...
Hot on the tail of Bump Hero, ZPlay is giving gamers another reason to get screen bashing with a brand new release. Tomb Heroes is a challenging action game in which you battle enemies in various tombs around the world. You can select from nine... | Read more »
Siralim 2 (RPG / Roguelike) (Games)
Siralim 2 (RPG / Roguelike) 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Siralim 2 is an old-school monster catching RPG. Summon and customize hundreds of creatures to fight for you as... | Read more »
Clean Text (Productivity)
Clean Text 1.0 Device: iOS Universal Category: Productivity Price: $3.99, Version: 1.0 (iTunes) Description: | Read more »
Gemini - A Journey of Two Stars (Games)
Gemini - A Journey of Two Stars 1.0.1 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.1 (iTunes) Description: *** SPECIAL LAUNCH SALE: $2.99 (25% off) *** "A mesmerizing and unexpectedly emotional journey." -- Los... | Read more »
How to get four NFL superstars for your...
Even though you're probably well on your way to building a top notch squad for the new season in Madden NFL Mobile, let's say you could beef it up by adding Rob Gronkowski, Antonio Brown, Von Miller, and Todd Gurley to your roster. That's... | Read more »
Cartoon Network Superstar Soccer: Goal!!...
Cartoon Network Superstar Soccer: Goal!!! – Multiplayer Sports Game Starring Your Favorite Characters 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Become a soccer superstar with your... | Read more »
NFL Huddle: What's new in Topps NFL...
Can you smell that? It's the scent of pigskin in the air, which either means that cliches be damned, pigs are flying in your neck of the woods, or the new NFL season is right around the corner. [Read more] | Read more »
FarmVille: Tropic Escape tips, tricks, a...
Maybe farming is passé in mobile games now. Ah, but farming -- and doing a lot of a other things too -- in an island paradise might be a little different. At least you can work on your tan and sip some pina coladas while tending to your crops. [... | Read more »
Become the King of Avalon in FunPlus’ la...
King Arthur is dead. Considering the legend dates back to the 5th century, it would be surprising if he wasn’t. But in the context of real-time MMO game King of Avalon: Dragon Warfare, Arthur’s death plunges the kingdom into chaos. Evil sorceress... | Read more »
Nightgate (Games)
Nightgate 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: *** Launch Sale: 25% OFF for a limited time! *** In the year 2398, after a great war, a network of intelligent computers known as... | Read more »

Price Scanner via MacPrices.net

9-inch 32GB iPad Pros on sale for $70 off MSR...
B&H Photo has 9″ 32GB WiFi Apple iPad Pros on sale for $70 off MSRP, each including free shipping. B&H charges sales tax in NY only: - 9″ Space Gray 32GB WiFi iPad Pro: $529 $70 off MSRP - 9... Read more
Mac minis on sale for up to $140 off MSRP
Adorama has Mac minis on sale for up to $100 off MSRP including free shipping plus NY & NJ sales tax only: - 1.4GHz Mac mini: $449 $50 off MSRP - 2.6GHz Mac mini: $649 $50 off MSRP Amazon has the... Read more
Back To School with OtterBox Essentials
Back to school means back to an environment that is tough on tech. OtterBox has the back to school essentials you need to keep tech safe from drops, bumps, scratches and hallway havoc. Check out the... Read more
VRS Design Releases New iPhone 7 Plus Case Li...
With a device as large and costly as the iPhone 7 Plus, it is primal instinct to protect it from potential damage. According to a study by SquareTrade in 2012, iPhone damages cost Americans roughly $... Read more
MacBook Airs on sale for up to $101 off MSRP
Amazon has 11″ and 13″ MacBook Airs on sale for up to $101 off MSRP for a limited time. Shipping is free: - 11″ 1.6GHz/128GB MacBook Air (model MJVM2LL/A): $798 $101 off MSRP - 11″ 1.6GHz/256GB... Read more
Apple certified refurbished iPad mini 4s avai...
Apple has certified refurbished iPad mini 4s now available for up to $120 off the cost of new models. An Apple one-year warranty is included with each iPad, and shipping is free. The following models... Read more
Apple price trackers, updated continuously
Scan our Apple Price Trackers for the latest information on sales, bundles, and availability on systems from Apple’s authorized internet/catalog resellers. We update the trackers continuously: - 15″... Read more
Global Tablet Shipments Projected to Increase...
Digitimes’ Jim Hsiao reports that global tablet shipments will increase by 16.3 percent sequentially to reach nearly 47 million units in 2016′s third quarter, but that volume will still be down over... Read more
Apple’s 2016 Back to School promotion: Free B...
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, and... Read more
Apple refurbished iPad Air 2s available start...
Apple has Certified Refurbished iPad Air 2 available starting at $339. Apple’s one-year warranty is included with each model, and shipping is free: - 128GB Wi-Fi iPad Air 2: $499 - 64GB Wi-Fi iPad... Read more

Jobs Board

*Apple* Solutions Consultant - Apple (United...
# Apple Solutions Consultant Job Number: 51443201 Mishawaka, Indiana, United States Posted: Aug. 25, 2016 Weekly Hours: 40.00 **Job Summary** As an Apple Read more
*Apple* Solutions Consultant - Apple (United...
# Apple Solutions Consultant Job Number: 51218354 Fredericksburg, Virginia, United States Posted: Aug. 18, 2016 Weekly Hours: 40.00 **Job Summary** As an Apple Read more
*Apple* Retail - Multiple Positions Birmingh...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
SW Engineer *Apple* TV - Apple Inc. (United...
The Apple TV team is looking for excellent software engineers with experience in hardware, media management, media playback, content delivery and a passion for Read more
*Apple* Retail - Multiple Positions Victor,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.