URL Launcher

All Databases MacTech Vol 12-1996

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 void init()

{

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:

URL Launcher

This applet creates a popup menu of URLs.

Referenced by (3):