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
$102.50
Apple Inc.
+0.25
MSFT
$45.43
Microsoft Corpora
+0.55
GOOG
$571.60
Google Inc.
+2.40

MacTech Search:
Community Search:

Software Updates via MacUpdate

VueScan 9.4.41 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
Cloud 3.0.0 - File sharing from your men...
Cloud is simple file sharing for the Mac. Drag a file from your Mac to the CloudApp icon in the menubar and we take care of the rest. A link to the file will automatically be copied to your clipboard... Read more
LibreOffice 4.3.1.2 - Free Open Source o...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
SlingPlayer Plugin 3.3.20.505 - Browser...
SlingPlayer is the screen interface software that works hand-in-hand with the hardware inside the Slingbox to make your TV viewing experience just like that at home. It features an array of... Read more
Get Lyrical 3.8 - Auto-magically adds ly...
Get Lyrical auto-magically add lyrics to songs in iTunes. You can choose either a selection of tracks, or the current track. Or turn on "Active Tagging" to get lyrics for songs as you play them.... Read more
Viber 4.2.2 - 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,... Read more
Cocktail 7.6 - General maintenance and o...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
LaunchBar 6.1 - Powerful file/URL/email...
LaunchBar is an award-winning productivity utility that offers an amazingly intuitive and efficient way to search and access any kind of information stored on your computer or on the Web. It provides... Read more
Maya 2015 - Professional 3D modeling and...
Maya is an award-winning software and powerful, integrated 3D modeling, animation, visual effects, and rendering solution. Because Maya is based on an open architecture, all your work can be scripted... Read more
BBEdit 10.5.12 - Powerful text and HTML...
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

This Week at 148Apps: August 25-29, 2014
Shiny Happy App Reviews   | Read more »
Qube Kingdom – Tips, Tricks, Strategies,...
Qube Kingdom is a tower defense game from DeNA. You rally your troops – magicians, archers, knights, barbarians, and others – and fight against an evil menace looking to dominate your kingdom of tiny squares. Planning a war isn’t easy, so here are a... | Read more »
Qube Kingdom Review
Qube Kingdom Review By Nadia Oxford on August 29th, 2014 Our Rating: :: KIND OF A SQUARE KINGDOMUniversal App - Designed for iPhone and iPad Qube Kingdom has cute visuals, but it’s a pretty basic tower defense game at heart.   | Read more »
Fire in the Hole Review
Fire in the Hole Review By Rob Thomas on August 29th, 2014 Our Rating: :: WALK THE PLANKUniversal App - Designed for iPhone and iPad Seafoam’s Fire in the Hole looks like a bright, 8-bit throwback, but there’s not enough booty to... | Read more »
Alien Creeps TD is Now Available Worldwi...
Alien Creeps TD is Now Available Worldwide Posted by Ellis Spice on August 29th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Dodo Master Review
Dodo Master Review By Jordan Minor on August 29th, 2014 Our Rating: :: NEST EGGiPad Only App - Designed for the iPad Dodo Master is tough but fair, and that’s what makes it a joy to play.   | Read more »
Motorsport Manager Review
Motorsport Manager Review By Lee Hamlet on August 29th, 2014 Our Rating: :: MARVELOUS MANAGEMENTUniversal App - Designed for iPhone and iPad Despite its depth and sense of tactical freedom, Motorsport Manager is one of the most... | Read more »
Motorsport Manager – Beginner Tips, Tric...
The world of Motorsport management can be an unforgiving and merciless one, so to help with some of the stress that comes with running a successful race team, here are a few hints and tips to leave your opponents in the dust. | Read more »
CalPal Update Brings the App to 2.0, Add...
CalPal Update Brings the App to 2.0, Adds Lots of New Stuff Posted by Ellis Spice on August 29th, 2014 [ permalink ] | Read more »
Baseball Battle Review
Baseball Battle Review By Jennifer Allen on August 29th, 2014 Our Rating: :: SIMPLE HITTINGUniversal App - Designed for iPhone and iPad Simple and cute, Baseball Battle is a fairly fun baseball game for those looking for something... | Read more »

Price Scanner via MacPrices.net

Labor Day Weekend MacBook Pro sale; 15-inch m...
B&H Photo has the new 2014 15″ Retina MacBook Pros on sale for up to $125 off MSRP. Shipping is free, and B&H charges NY sales tax only. They’ll also include free copies of Parallels Desktop... Read more
Labor Day Weekend iPad mini sale; $50 to $100...
Best Buy has the iPad mini with Retina Display (WiFi models) on sale for $50 off MSRP on their online store for Labor Day Weekend. Choose free shipping or free local store pick up. Price is for... Read more
13-inch 1.4GHz MacBook Air on sale for $899,...
Adorama has the new 2014 13″ 1.4GHz/128GB MacBook Air on sale for $899.99 including free shipping plus NY & NJ tax only. Their price is $100 off MSRP. Read more
It’s Official: Apple Issues Invitations To Se...
Apple has issued one of its characteristically cryptic press invitations for a special event to be held at the Flint Center for the Performing Arts in hometown Cupertino on Sept. 9, 2014 at 10:00 am... Read more
Tablet Shipments To See First On-year Decline...
TrendForce analyst Caroline Chen notes that when the iPad launched in 2010, it was an instant hit and spurred a tablet PC revolution, with tablets so popular that that notebook PC sales stagnated and... Read more
SOBERLINK Releases Apple iOS Compatible Handh...
Cypress, California based SOBERLINK, Inc., creator of the first handheld Breathalyzer designed to improve recovery outcomes, continues to show prominence in the mobile alcohol monitoring space with... Read more
New 21″ 1.4GHz iMac on sale again for $999, s...
Best Buy has the new 21″ 1.4GHz iMac on sale for $999.99 on their online store. Their price is $100 off MSRP. Choose free shipping or free local store pick up. Price is for online orders only, in-... Read more
Smartphone Outlook Remains Strong for 2014, U...
According to a new mobile phone forecast from the International Data Corporation (IDC) Worldwide Quarterly Mobile Phone Tracker, more than 1.25 billion smartphones will be shipped worldwide in 2014,... Read more
Save up to $60 with Apple refurbished iPod to...
The Apple Store has Apple Certified Refurbished 5th generation iPod touches available starting at $149. Apple’s one-year warranty is included with each model, and shipping is free. Many, but not all... Read more
12-Inch MacBook Air Coming in 4Q14 or 2015 –...
Digitimes’ Aaron Lee and Joseph Tsai report that according to Taiwan-based upstream supply chain insiders, Apple plans to launch a thinner MacBook model either at year end 2014 or in 2015, and that... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.