Network Mobility: The Design Center of Java

Network-mobile Java software can come in many forms besides just the two forms, Java applets and Jini service objects, described in the previous sections. Yet although network-mobile Java is not limited to applets and service objects, the framework that supports any other form of network-mobile Java will likely look similar to the framework that supports applets and service objects. Like applets and service objects, for example, other forms of network-mobile Java will execute in the context of a host Java application, and the class files for the network-mobile Java code will be loaded by user-defined class loaders. User-defined class loaders can download class files across a network in custom ways that bootstrap class loaders usually can't. And because network-mobile class files are not always known to be trustworthy, the separate name-spaces provided by user-defined class loaders are needed to protect malicious or buggy code from interfering with code loaded from other sources. Lastly, because network-mobile class files can't always be trusted, there will generally be a security manager or access controller establishing a security policy for the network- mobile code.

The key to understanding Java's architecture, then, is to see enabling the network mobility of code and objects as the design center of Java. Although Java can offer valuable benefits, such as increased programmer productivity and increased program robustness, in situations that don't even remotely involve a network, the main focus of Java's architecture is the network. The Java virtual machine, Java class file, Java API, and Java programming language work in concert to make network mobile software both possible and practical. Through its support for network mobile code and objects, Java helps software developers meet challenges and seize opportunities presented by the ever-progressing network age.

The Resources Page

For links to information about other examples of network-mobile Java, see the resources page: http://www.artima.com/insidejvm/resources.