1.7. Java and the Web
The application-level safety features of Java make it possible to develop new kinds of applications that were not
In addition to applets, a more recent model for Internet downloadable application content is Java Web Start. The Web Start API allows your web browser to install applications locally, with security still enforced by the Java runtime system. This system can also automatically update the software when it is used. We'll discuss this more in Chapter 23.
As far as the web browser model is
A Java applet is a compiled Java program,
An applet has a four-part life cycle. When an applet is initially loaded by a web browser, it's asked to initialize itself. The applet is then informed each time it's displayed and each time it's no longer visible to the user. Finally, the applet is told when it's no longer needed, so that it can clean up after itself. During its lifetime, an applet
Figure 1-4. Applets in a web document
may start and suspend itself, do work, communicate with other applications, and interact with the web browser.
Applets are autonomous programs, but they are confined within the walls of a web browser or applet viewer and have to play by its rules. We'll be discussing the details of what applets can and can't do as we explore features of the Java language. However, under the most conservative security policies, an applet can interact only with the user and can communicate over the network only with the host from which it originated. Other types of activities, such as accessing files or interacting directly with outside applications, are typically prevented by the security manager that is part of the web browser or applet viewer. But aside from these restrictions, there is no fundamental difference between a Java applet and a standalone Java application.
1.7.2. New Kinds of Media
When it was first released, Java quickly achieved a reputation for multimedia capabilities. Frankly, this wasn't really deserved. At that point, Java provided facilities for doing simple animations and playing audio (which was leaps and bounds beyond static web pages). You could animate and play audio
Java's multimedia capabilities have now taken shape. Java now has CD-quality sound, 3D animation, media players that synchronize audio and video, speech synthesis and recognition, and more. The Java Media Framework now supports most common audio and video file formats; the Java Sound API (part of the
1.7.3. New Software Development Models
For many years, people have been using integrated development environments (
For visual development environments to work well, you need to be able to create reusable software components. That's what the JavaBeans architecture is all about: it defines a way to package software as reusable building blocks. A graphical development tool can figure out a component's capabilities, customize the component, and connect it to other components to build applications. In theory, JavaBeans extends the idea of graphical development a step further. JavaBeans components, called beans, aren't limited to visible, user interface components: you can have beans that are entirely invisible and whose job is purely computational. For example, you can have a bean that does database access; you can connect this to a bean that lets the user request information from the database; and you can use another bean to display the result. You can also have a set of beans that implement the functions in a mathematical library; you can then do numerical analysis by connecting different functions to each other. In either case, the idea is that you can create programs without writing a great deal of code using beans from a variety of sources.
While this style of visual programming hasn't proven itself much outside of GUI development yet, elements of JavaBeans are seen throughout the Java libraries,
In this book, we'll take a look at the NetBeans