6.6 QA: A time to recap and reflect

A: Java is a platform-independent, highly object-oriented, third-generation programming language and software development methodology developed by Sun. Though its origins predate the advent of the Web, Java was introduced to the world in 1995 as a strategic technology for realizing dynamic, interactive Web applications.

A: Yes and no. It is not a bona fide industry standard maintained by a recognized standards organization. Instead, Sun still controls much of what happens to and with Java, though there is an egalitarian, open-to-all mechanism, known as the Java Community Process (JCP), where anybody can participate in the evolutionary process of Java. The Java specifications are also freely open to all and there are free, open-source reference implementations of these specifications. Consequently, a large and influential segment of the software development community, including those associated with powerful open -source movements such as Apache, is willing to treat Java as at least a de facto standard despite Sun s stewardship of it.

A: Yes. The latest version of the server-side Java specification, J2EE 1.4, includes extensive support for XML and Web services via a series of APIs for XML document parsing, SOAP-based XML document transmission, UDDI access, and RPC invocation with SOAP. All of these Web services “ related APIs are packaged and available for free, along with other complementary software, such as user -interface creation technology JavaServer Faces (JCF), with the Java Web Services Developer Pack (Java WSDP) 1.2.

A: Java applications are conventional, stand-alone programs, installed and executed off a system s hard drive in the same way as applications developed with other languages ”with one distinguishing feature being, however, that Java applications can be readily ported between vastly disparate systems. They could typically be invoked via a command-line instruction and, in common with other applications, will normally have unfettered access to the host system s resources (e.g., data files). Applets, though similar to applications, are not considered to run in stand-alone mode. Instead, an applet is a program that runs within a Web browser or an applet viewer and, moreover, has strictly limited access to host resources, in particular any kinds of files. An applet, as such, is meant to be nonmalicious at all costs. This intentional restricted access to host resources precludes the danger of applets being used to propagate viruses or worms.

A: Java applications as well as Java applets were said to execute on Java Virtual Machines (JVMs). A JVM is thus a run-time (or execution) environment. JVMs are implemented on various computing platforms, in particular Web browsers, and all popular operating systems ranging from mainframe z/OS to the Mac OS. Though the concept of JVMs is still very much a part of the Java culture, today JVMs are referred to as containers.

A: J2EE is the Java 2 Platform, Enterprise Edition. A Java platform is said to consist of a JVM (or container) and a series of standard libraries, which are referred to as the Java API. Today there are three Java 2 platforms, with J2EE being one of them. The other two are J2SE, the standard edition of the platform targeted at client-side implementations, and J2ME, a micro-edition meant for embedded applications in devices such as cell phones and TV set-top boxes.

A: Most certainly . Though Microsoft, in a fit of pique with Sun related to Java licensing, has claimed that it would no longer be including a built-in Java run-time environment within Windows, starting in early 2004, free versions of the necessary Windows software are readily and conveniently available from java.sun.com and www.java.com.

A: JavaServer Pages (JSPs) decouple the user-interface aspects of Web applications from that of content generation. JSP thus enables Web developers to change the presentation layout of a Web page or the contents of that Web page independently of each other. JSPs are somewhat analogous to the now relatively common Microsoft Active Server Pages (ASPs). The big difference, as ever, is that ASPs are Microsoft IIS “centric, whereas JSPs are meant to work with any Web server. JSPs are built on top of Java servlet technology ”where a servlet is in essence a server-side applet. JSPs neatly demarcate HTML from servlet code.

A: Most definitely. So-called reference implementations of the Java platforms are available from java.sun.com for Windows, Solaris, and RedHat Linux platforms. Other vendors , such as H-P and IBM, provide platform-specific implementations for their particular systems. In addition, Sun provides an entry-level version of its Sun ONE Application Server on a no-charge basis, as does a company called JBoss (www.jboss.org). No-charge, open-source Java-related software is also readily available from Apache.

A: A Java application server, which typically refers to a commercial product, though the no-charge JBoss offering is also called an application server, is a value-added, platform-specific implementation of a particular J2EE specification. Commercial application servers offer extensive load-balancing, failover, and system clustering support as well as optimized drivers for specific commercial database systems. They include back-end connectors (or adapters) to existing applications as well as graphical application deployment and management capabilities.