TweetFollow Us on Twitter

Java Popup
Volume Number:12
Issue Number:7
Column Tag:Getting Started

A Java Popup Menu URL Launcher

By Dave Mark

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

Since last month’s column, I’ve been consumed with Java. I’ve been reading every Java book I could get my hands on, including the galleys for Learn Java on the Macintosh (Addison-Wesley), Java in a Nutshell (O’Reilly & Associates), Active Java (Addison-Wesley), Java Essentials for C and C++ Programmers (Addison-Wesley), and Teach Yourself Java for Macintosh In 21 Days (Hayden). There are lots of Java books out there, some of them much better than others.

Beware of Java books written to pre-release versions of the Java SDK from Sun. Much has changed between the pre-release and release versions and, as a slew of messages on the net will attest, those changes will frustrate you as you attempt to get the book sample code to work.

The applets from Learn Java on the Macintosh and Java in a Nutshell have been translated into Metrowerks’ Java project format. You can download the applets from Metrowerks’ Web site (www.metrowerks.com).

This Month’s Applets

One important use of Java is to extend the functionality of a Web site, beyond the capabilities offered by HTML. If you’ve ever been to Netscape’s Web site, you’ve probably encountered the long list of download sites that allow you to download the latest version of a Netscape product (Figure 1).

If you’ve got a long list of URLs to put on your Web site, you can, of course, represent them just like Netscape did, as a long series of links. The downside to this approach is that the links can take up a fair amount of screen space. An alternative is to use a form CGI and represent the list as a popup menu of URLs.

Figure 1. The long list of sites to download the latest version of Netscape Navigator

Solving the problem using a CGI is fine, but I wanted to implement this “popup” solution as a Java applet instead. To do this, we need to take advantage of the existing Java applet model, as embodied in the java.applet.Applet class. To make this a little easier to understand, I developed the applet in two stages. Here’s the first version:

import java.applet.*;
import java.awt.*;
import java.net.*;

public class popup extends Applet
{
 private Choice  urlChoices;
 int    numURLs;
 
 public voidinit()
 {
 this.setBackground( Color.yellow );//java.awt.Color
 this.setForeground( Color.red );//java.awt.Color
 
 urlChoices = new Choice();
 
 urlChoices.addItem( "www.metrowerks.com" );
 urlChoices.addItem( "www.netscape.com" );
 urlChoices.addItem( "www.mactech.com" );
 
 urlChoices.setForeground( Color.green );
 urlChoices.setBackground( Color.blue );
 
 this.add( new Label( "Select URL: " ) );
 this.add( urlChoices );
 }
 
 public boolean action( Event e, Object obj )
 {
 URL    url;
 
 if ( e.target == urlChoices )
 {
 try
 {
 url = new URL( obj.toString() );
 }
 catch( MalformedURLException err )
 {
    // Could print error message here.
 return true;
 }
 this.getAppletContext().showDocument( url );
 return true;
 }
 else
 return super.action( e, obj );
 }
}

Since I’m using CodeWarrior, I started by creating a new project file called popup.µ using the Java applet stationery. Next, I created a new source code file named popup.java and added it to the project. I typed in my source code, saved it, then selected the .java file in the project window and compiled it. The compiler used my Java source code to produce a file named popup.class which contains the Java byte code that will be loaded by my HTML file.

Speaking of my HTML file, I used CodeWarrior to create a new file called popup.html and saved it in the same folder as my other project files. I didn’t add the HTML file to the project. Here’s the HTML:

<HTML>
<HEAD>
<TITLE>URL Launcher</TITLE>
</HEAD>
<BODY>
This applet creates a popup menu of URLs.
<H>R
<APPLET CODE="popup.class" WIDTH=300 HEIGHT=35>
</APPLET>
</BODY>
</HTML>

If you’ve never seen HTML before, it’s pretty straightforward. Basically, your HTML file contains the text you want to appear on your Web page, with a bunch of “tags” sprinkled throughout that define how the text looks. A tag is a pair of angle brackets that enclose a tag name, along with optional tag attributes. Some tags work in pairs. An end tag always starts with a '/'.

For example, to define the title of a particular page, you’ll start with the <title> tag, follow it with the title, then follow the text with the </title> tag. The <hr> tag places a horizontal rule on your page. Note that the <hr> tag doesn’t require a corresponding </hr> tag, since there is no text that needs to be surrounded. By the way, HTML tags are case-insensitive.

The <applet> tag is the tag we’re interested in in this column. The CODE attribute specifies the name of the class file we want launched. In this case, we want the Java byte codes in popup.class executed.

Drag the HTML file on top of your favorite Java applet runner. If you have a Java-capable browser (like Netscape Atlas), you can open the HTML file and see how your applet looks on an actual Web page. Alternatively, if you run the applet using an applet runner, you’ll see the applet portion of the Web page only. Most applet runners only understand the applet tag and will ignore the rest of the HTML.

Figure 2 shows the popup applet as viewed in an early beta of Netscape Atlas. As long as your Internet connection is live, selecting a URL from the popup menu transfers you to that URL.

Figure 2. Our popup applet in action

Let’s take a look at the source code...

The Popup.java Source Code

As I already mentioned, this applet extends the java.applet.Applet class. Go into the API Documentation folder that came with your development environment and use your Web browser to open the file java.applet.Applet.html. As you’ll see in the figure at the top of the page, java.applet.Applet is derived from java.awt.Panel, which is derived from java.awt.Container, which is derived from java.awt.Component. java.awt.Component is where all the action is. That’s where you’ll find all the interesting methods used by most applets. Spend a little quality time with java.awt.Component.html. It will definitely pay off.

The first few lines make the classes in java.applet.*, java.awt.*, and java.net.* available to our program. This allows us to refer to Applet instead of java.applet.Applet and URL instead of java.net.URL. You get the idea.

import java.applet.*;
import java.awt.*;
import java.net.*;

Our popup class extends the Applet class. We declare the variable urlChoices inside our class. urlChoices is a reference to a Choice (Java’s term for a popup menu).

public class popup extends Applet
{
 private Choice  urlChoices;

The first method in our applet is the init() method. init() will be called automatically when our applet is started up. We’ll use this method to set up our Choice popup menu. We’ll start off by setting the applet background color to yellow and the foreground color to red. Note that this refers to the applet. If you take a look at Figure 2, you’ll see that the background is yellow and that the popup menu’s label text is red. I know yellow and red might not be a particularly good looking combination, but it does make the point, right?

 public voidinit()
 {
 this.setBackground( Color.yellow );//java.awt.Color
 this.setForeground( Color.red );//java.awt.Color

The next line uses new to create a new Choice object. Note that urlChoices is set to null until the new Choice is created.

 urlChoices = new Choice();

Next, the Choice classes’ addItem() method is called to add three URLs to the project. The popup menu’s foreground and background colors are set, too, but these calls don’t seem to have any effect.

 urlChoices.addItem( "www.metrowerks.com" );
 urlChoices.addItem( "www.netscape.com" );
 urlChoices.addItem( "www.mactech.com" );
 
 urlChoices.setForeground( Color.green );
 urlChoices.setBackground( Color.blue );

Finally, a new Label object is created and the Label and Choice objects are added to the applet.

 this.add( new Label( "Select URL: " ) );
 this.add( urlChoices );
 }

The action() method is called whenever an event occurs that relates to the applet. We’ll declare a URL reference to hold the URL we want to transfer to.

 public boolean action( Event e, Object obj )
 {
 URL    url;

The Event object e contains the event description we are responding to. Check out java.awt.Event to get a sense of Java event handling. e.target specifies the target object of the event. If the target is our popup menu, urlChoices, we’ll handle the event. Otherwise, we’ll pass the event on to our superclass and return whatever value super.action() returns.

If urlChoices was the target, we’ll try creating a new URL object. Some Java objects require that you catch exceptions thrown by the object. To get a sense of this, go to the java.net.URL.html page. Note that all of the constructors throw the MalformedURLException error. You must catch this exception or your code won’t compile. We ignore the error, but we could print an error message or, better yet, put up a dialog letting users know that the URL they selected isn’t quite right.

If you throw an exception, you’ll create a new java.lang.exception object (or some class that extends throwable). But when you catch an exception, the exception object is passed to your catch block, as err was in this case. Take a look at java.lang.Throwable.html, especially the getMessage() method.

 if ( e.target == urlChoices )
 {
 try
 {

Since the event target is our popup menu, the object will be the menu itself. By calling the method toString() (inherited from Object), we’ll get a string with the popup menu’s current setting. We’ll then use that string to initialize the URL.

 url = new URL( obj.toString() );
 }
 catch( MalformedURLException err )
 {
 // Could print error message here.
 return true;
 }

Assuming the URL object was created okay, we’ll call getAppletContext() to get our applet’s context, then use that object to call showDocument(), which will tell our browser to jump to a different URL.

 this.getAppletContext().showDocument( url );
 return true;
 }
 else
 return super.action( e, obj );
 }
}

Same Applet, Using Parameters

Here’s a second version of the applet that gets its URLs from the HTML file. To see how this works, take a look at the second version of our HTML file:

<HTML>
<HEAD>
<TITLE>URL Launcher</TITLE>
</HEAD>
<BODY>
This applet takes a series of parameters and turns them into a popup 
menu of URLs. The PARAM with the name numURLs tells you how many URLs 
are included. PARAM "1" contains the 1st URL, PARAM "2" contains the 
next URL, etc.
<H>R
<APPLET code="popup.class" width=300 height=35>
<PARAM name="numURLs" value="3">
<PARAM name="1" value="http://www.metrowerks.com">
<PARAM name="2" value="http://www.mactech.com">
<PARAM name="3" value="http://www.netscape.com">
</APPLET>
</BODY>
</HTML>

Notice that we’ve added a series of <PARAM> tags between the <APPLET> and </APPLET> tags. Each PARAM passes a named parameter to our applet. The numURLs parameter tells our applet how many URLs we are passing in. The 1 parameter contains the first URL, 2 contains the second URL, etc.

Here’s the second version of our applet:

import java.applet.*;
import java.awt.*;
import java.net.*;

public class popup extends Applet
{
 private Choice  urlChoices;
 
 public voidinit()
 {
 int    numURLs = 0;
 
 this.setBackground( Color.yellow );//java.awt.Color
 this.setForeground( Color.red );//java.awt.Color
 
 urlChoices = new Choice();
 
 urlChoices.setForeground( Color.green );
 urlChoices.setBackground( Color.blue );
 
 String numURLsString = this.getParameter( "numURLs" );
 
 if ( numURLsString == null )
 {
 this.showStatus( "null or missing numURLs Parameter!" );
 }
 else
 {
 try
 {
 numURLs = Integer.parseInt( numURLsString );
 }
 catch( NumberFormatException err )
 {
 numURLs = 0;
 this.showStatus( "Bad numURLs Parameter: " +                  
   numURLsString );
 }
 
 String urlString;
 
 for ( int i=1; i<=numURLs; i++ )
 {
 urlString = this.getParameter( Integer.toString( i ) );
 
 if ( urlString == null )
 this.showStatus( "Missing Parameter: " + i );
 else
 urlChoices.addItem( urlString );
 }
 }
 
 this.add( new Label( "Select URL: " ) );
 this.add( urlChoices );
 }
 
 public boolean action( Event e, Object obj )
 {
 URL    url;
 
 if ( e.target == urlChoices )
 {
 try
 {
 url = new URL( obj.toString() );
 }
 catch( MalformedURLException err )
 {
    // Could print error message here.
 return true;
 }
 this.getAppletContext().showDocument( url );
 return true;
 }
 else
 return super.action( e, obj );
 }
}

Basically, the difference here is in this chunk of code from init():

 String numURLsString = this.getParameter( "numURLs" );
 
 if ( numURLsString == null )
 {
 this.showStatus( "null or missing numURLs Parameter!" );
 }
 else
 {
 try
 {
 numURLs = Integer.parseInt( numURLsString );
 }
 catch( NumberFormatException err )
 {
 numURLs = 0;
 this.showStatus( "Bad numURLs Parameter: " +                  
  numURLsString );
 }
 
 String urlString;
 
 for ( int i=1; i<=numURLs; i++ )
 {
 urlString = this.getParameter( Integer.toString( i ) );
 
 if ( urlString == null )
 this.showStatus( "Missing Parameter: " + i );
 else
 urlChoices.addItem( urlString );
 }
 }
 
 this.add( new Label( "Select URL: " ) );
 this.add( urlChoices );

We start by calling getParameter() to retrieve the numURLs parameter. If the parameter is missing, we call showStatus() to display an error message in the browser’s status message area. If the parameter was there, we’ll try parsing an integer value from the string, placing the value in numURLs. Assuming we get a proper number, we’ll step from 1 to numURLs.

Inside the loop, we’ll convert the current index into a string (using Integer.toString()) and pass that string into getParameter(). If that parameter exists, we’ll add that parameter into the popup menu.

Till Next Month...

Want more Java? Want more PowerPlant? Want some TCL? What the heck do you want? Send me some email. Let me know. Otherwise, I’ll just keep writing about Java until I get sick of it! <g> By the way, I hope that you will take a moment and visit www.zumacafe.com, the Web site for a brand new internet cafe in Santa Fe, New Mexico. Zuma’s is the brainchild of Robin Williams, a brilliant writer and someone who has given a great deal to the Macintosh community. Check out the site and, if you get to Santa Fe, drop by Zuma’s and say hello!

 
AAPL
$98.38
Apple Inc.
-0.64
MSFT
$43.89
Microsoft Corpora
-0.09
GOOG
$585.61
Google Inc.
-4.99

MacTech Search:
Community Search:

Software Updates via MacUpdate

Drive Genius 3.2.4 - Powerful system uti...
Drive Genius is an OS X utility designed to provide unsurpassed storage management. Featuring an easy-to-use interface, Drive Genius is packed with powerful tools such as a drive optimizer, a... Read more
Vitamin-R 2.15 - Personal productivity t...
Vitamin-R creates the optimal conditions for your brain to work at its best by structuring your work into short bursts of distraction-free, highly focused activity alternating with opportunities for... Read more
Toast Titanium 12.0 - The ultimate media...
Toast Titanium goes way beyond the very basic burning in the Mac OS and iLife software, and sets the standard for burning CDs, DVDs, and now Blu-ray discs on the Mac. Create superior sounding audio... Read more
OS X Yosemite Wallpaper 1.0 - Desktop im...
OS X Yosemite Wallpaper is the gorgeous new background image for Apple's upcoming OS X 10.10 Yosemite. This wallpaper is available for all screen resolutions with a source file that measures 5,418... Read more
Acorn 4.4 - Bitmap image editor. (Demo)
Acorn is a new image editor built with one goal in mind - simplicity. Fast, easy, and fluid, Acorn provides the options you'll need without any overhead. Acorn feels right, and won't drain your bank... Read more
Bartender 1.2.20 - Organize your menu ba...
Bartender lets you organize your menu bar apps. Features: Lets you tidy your menu bar apps how you want. See your menu bar apps when you want. Hide the apps you need to run, but do not need to... Read more
TotalFinder 1.6.2 - Adds tabs, hotkeys,...
TotalFinder is a universally acclaimed navigational companion for your Mac. Enhance your Mac's Finder with features so smart and convenient, you won't believe you ever lived without them. Tab-based... Read more
Vienna 3.0.0 RC 2 :be5265e: - RSS and At...
Vienna is a freeware and Open-Source RSS/Atom newsreader with article storage and management via a SQLite database, written in Objective-C and Cocoa, for the OS X operating system. It provides... Read more
VLC Media Player 2.1.5 - Popular multime...
VLC Media Player is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, MP3, OGG, ...) as well as DVDs, VCDs, and various streaming protocols. It... Read more
Default Folder X 4.6.7 - Enhances Open a...
Default Folder X attaches a toolbar to the right side of the Open and Save dialogs in any OS X-native application. The toolbar gives you fast access to various folders and commands. You just click... Read more

Latest Forum Discussions

See All

Note Review
Note Review By Jennifer Allen on July 29th, 2014 Our Rating: :: TOO SIMPLEiPhone App - Designed for the iPhone, compatible with the iPad Note is a note taking app that’s a little too short on features to be worth its asking price... | Read more »
Chainsaw Warrior Goes on Sale & Ther...
Chainsaw Warrior Goes on Sale & There’s a Chance to Win a Copy of the Original Board Game Posted by Jennifer Allen on July 29th, 2014 [ permalink | Read more »
It Came From Canada: Tiny Tower Vegas
If you go to a casino, you might make a lot of money. If you run a casino, you’re guaranteed to make a lot of money. The choice seems pretty obvious. So while waiting for your shady real estate deals to move forward, get prepared with Tiny Tower... | Read more »
Z Hunter Review
Z Hunter Review By Lee Hamlet on July 29th, 2014 Our Rating: :: RIGHT ON TARGETUniversal App - Designed for iPhone and iPad While it might not necessarily break new ground, Z Hunter has enough tricks up its sleeve to ensure that... | Read more »
Huge Update Comes To Duet, Adding 48 New...
Huge Update Comes To Duet, Adding 48 New Stages Posted by Jennifer Allen on July 29th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Sharknado: The Video Game Available Now....
Sharknado: The Video Game Available Now. Seriously. Posted by Rob Rich on July 29th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Frog Orbs 2 Review
Frog Orbs 2 Review By Nadia Oxford on July 29th, 2014 Our Rating: :: THIS MAGIC IS A TAD MONOTONOUS Universal App - Designed for iPhone and iPad Frog Orbs 2 is repetitive, but younger players should enjoy it nonetheless.   | Read more »
Puzzix Review
Puzzix Review By Jennifer Allen on July 29th, 2014 Our Rating: :: NICE IDEAUniversal App - Designed for iPhone and iPad A little like Tetris, Puzzix is all about piecing together blocks and watching them vanish. It could do with... | Read more »
Cannonball eMail is Now Live – Works Wit...
Cannonball eMail is Now Live – Works With Gmail, Yahoo, Outlook, Hotmail, and AOL Posted by Jessica Fisher on July 29th, 2014 [ permalink ] | Read more »
To The End Review
To The End Review By Lee Hamlet on July 29th, 2014 Our Rating: :: A VICIOUS CYCLEUniversal App - Designed for iPhone and iPad To The End will test players’ patience, timing, and dedication as they try to navigate all 13 levels in... | Read more »

Price Scanner via MacPrices.net

Apple Updates MacBook Pro with Retina Display...
Apple today updated its MacBook Pro with Retina display with faster processors and double the amount of memory in both entry-level configurations. MacBook Pro with Retina display features a Retina... Read more
Up to $250 price drop on leftover 15-inch Mac...
B&H Photo has dropped prices on 2013 15″ Retina MacBook Pros by as much as $250 off original MSRP. Shipping is free, and B&H charges NY sales tax only: - 15″ 2.3GHz Retina MacBook Pro: $2349... Read more
Updated MacBook Pro Price Trackers
We’ve updated our MacBook Pro Price Trackers with the latest information on prices, bundles, and availability on the new 2014 models from Apple’s authorized internet/catalog resellers as well as... Read more
Apple updates MacBook Pros with slightly fast...
Apple updated 13″ and 15″ Retina MacBook Pros today with slightly faster Haswell processors. 13″ models now ship with 8GB of RAM standard, while 15″ MacBook Pros ship with 16GB across the board. Most... Read more
Apple drops price on 13″ 2.5GHz MacBook Pro b...
The Apple Store has dropped their price for the 13″ 2.5GHz MacBook Pro by $100 to $1099 including free shipping. Read more
Apple drops prices on refurbished 2013 MacBoo...
The Apple Store has dropped prices on Apple Certified Refurbished 13″ and 15″ 2013 MacBook Pros, with model now available starting at $929. Apple’s one-year warranty is standard, and shipping is free... Read more
iOS 8 and OS X 10.10 To Support DuckDuckGo As...
Writing for Quartz, Dan Frommer reports that Apple’s forthcoming iOS 8 and OS X 10.10 operating systems version updates will allow users to select DuckDuckGo as their default search engine. He notes... Read more
U.K. Hospital Using iPods and iPads To Record...
British news journal GazetteLive’s. Ian McNeal notes that the old “an apple a day keeps the doctor away” proverb is being turned on its head at http://southtees.nhs.uk/hospitals/james-cook/ James... Read more
13-inch 2.5GHz MacBook Pro on sale for $1099,...
Best Buy has the 13″ 2.5GHz MacBook Pro available for $1099.99 on their online store. Choose free shipping or free instant local store pickup (if available). Their price is $100 off MSRP. Price is... Read more
Roundup of Apple refurbished MacBook Pros, th...
The Apple Store has Apple Certified Refurbished 13″ and 15″ MacBook Pros available for up to $400 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free. Their prices... Read more

Jobs Board

Sr Software Lead Engineer, *Apple* Online S...
Sr Software Lead Engineer, Apple Online Store Publishing Systems Keywords: Company: Apple Job Code: E3PCAK8MgYYkw Location (City or ZIP): Santa Clara Status: Full Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Sr. Product Leader, *Apple* Store Apps - Ap...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.