This article will show you how to create an interactive, graphics-based applet by designing only the graphical objects themselves and by specifying their behavior given some external event (i.e., a mouse click or a button press). The ipl and ipl.graphics classes and interfaces will let you design with both notification and interfaces, in order to coordinate communication between your graphical objects and between the graphical objects and the display medium (i.e., a canvas object). This article will also show you how to 'wire-up' your interactive applet to buttons in order to give the user control over your graphical objects.

Consider an Internet client that wants to connect to a site which allows access only to trusted clients. Consider a trusted client that has access to the site. Wouldn't it be great if the trusted client could relay the Internet client's data to the restricted-access site? In other words, it could act as a 'channel', or a 'router', for a restricted site. This article describes JTRouter - a multi-threaded Java program that acts as a tunnel for socket communication between an Internet client and a remote server. JTRouter allows a machine to initiate as well as accept Internet connections in independent threads. It is a unique implementation in that both the client and the server roles are implemented in the same process.

'Hi, everybody!' the large programmer/teacher announces as he bounces into a class full of aspiring Java programmers. 'Welcome to Java.' My name is John Tabbone. I teach Java at NYU's Information Technologies Institute. ITI is a professional program and the students who enroll in my course typically have a diverse skill set. The usual makeup of a class includes C++ programmers, VB and PB developers, Cobol/Mainframe people and a few people whose only programming experience is seeing the new Java commercials. We run the gamut. But beneath the variety of technical backgrounds is the common desire to learn about Java.

The Java programming language and platform are revolutionizing the development and deployment of distributed software. I believe that the huge 'twitch' game market (based on game consoles and PCs) will continue to grow, but the largest market growth eventually will be in distributed games and entertainment experiences. With steady improvements in runtime performance, Java is well positioned to be the language of choice for writing distributed entertainment software.

The Observer Design Pattern is among the most useful for object-oriented software design. The JDK itself makes heavy use of a variant of this pattern in the 1.1 AWT event delegation model. The JDK also provides a reusable embodiment of the pattern in the form of the java.util.Observer interface and the java.util.Observable class. If you've done much serious Java programming you've more than likely had occasion to use these classes.

The following questions on JavaBeans were recently asked of Andy Nguyen, Senior Product Marketing Manager, Authoring and Development Tools, Sun Microsystems, Inc.

It is possible to create a very attractive look-and-feel prototype of a Calendar-based browser application in JavaScript, but to compete with tough-minded mainframe legacy systems such as MEMO requires a highly functional and scalable working prototype to justify the continued investment and potential encapsulation of a large mainframe system.

By all accounts, 1996 was the year of Java. In that short year, Java made the transition from a humble, almost academic, cross-platform computing paradigm to becoming the virtual center of the Internet development world. The introduction of applets has helped drive the move from static Web pages to dynamic client-side processing.

Since Java's explosion into the marketplace, we've seen a flood of development tools, wizards and environments. The heavy hitters in this area seem to be Symantec and Microsoft, with Café taking the visual approach to development and Microsoft's Visual J++ continuing Microsoft's terrifically successful line of Development Studio products.

Introduction With ever increasing software complexity, error handling mechanisms offered by programming languages become more and more important. Traditional error handling techniques such as using global variables to indicate an error (errno in C), returning a value that represents an error or simply terminating the program resulted in difficult to read and error-prone code.

It is possible to create a very attractive look-and-feel prototype of a Calendar-based browser application in JavaScript, but to compete with tough-minded mainframe legacy systems such as MEMO requires a highly functional and scalable working prototype to justify the continued investment and potential encapsulation of a large mainframe system.

Build Java Applications Faster and Easier Business today moves at the speed of the Internet. Corporations are rapidly deploying Intranets as the vehicles for real-time information. But for professional developers, the wide adoption of the Internet has given rise to a new challenge: delivering high-quality applications, with limited resources, in a short time. The demand for information requires developers to deliver applications which reach more users, on a multitude of heterogeneous platforms, across global networks.

Introduction What if you built a Web site and nobody came? Or they came once and forgot to check in again to see all the latest stuff you built? One of the problems with the Web is that it has been hard to get people to become regular users of your site. You're either on the Favorites List or you're not. And even if you're there, there's no promise that people will think to call up your site each day.

Since the inception of the Internet, there has yet to be a topic as controversial as "Push". In fact, it's hard to pick up a trade journal that doesn't talk about it. So, without writing a dissertation on the value of "Push", let's explore an extension of this idea. "Managed Push" is a methodology that lets everyone in the information chain have the tools, access and security to obtain enterprise-wide data when, where and how they need it.

Organizations are implementing Internet strategies to speed up business cycles and gain a leg up on their competition. They are relying on the Internet "dial tone" - or Webtone - to enable global Web-based computing and provide them with the capabilities to run their day-to-day business faster, smarter and cheaper.

"Java is the language of network computing," said Lawrence J. Ellison, Chairman and Chief Executive Officer of Oracle Corporation. Basically, there are two main reasons as to why Java is the language of choice for network computing:

What Is An Intranet? If Intranets were made into a movie it would probably be called, "Honey, I Shrunk the Internet!" A simple definition of an Intranet is: bringing proven Internet technologies, such as Web servers, an ubiquitous networking protocol (namely TCP/IP), and other Internet protocols such as HTTP (Hyper Text Transfer Protocol), MIME (Multipurpose Internet Mail Extensions), SMTP (Simple Mail Transfer Protocol), etc., inside the walls of your company. Intranets can be used for:

Today, Web database publishing is an important way to publish information electronically. It actually combines the advantages of two important technologies - database and the Web. Standard database interfaces such as ODBC[1] (Open Database Connectivity) are used to provide an abstraction layer so that application programs can access data in a uniform and vendor-neutral way. ODBC is a standard API interface introduced by Microsoft. Each database requires a driver that converts SQL calls into the respective database's native calls and then performs the database interactions. Currently, there are many databases that come with ODBC drivers such as Oracle, Sybase, MS SQL, etc.

Scientific and technical software developers require the ability to "see" their data and do their analyses graphically instead of, or in addition to, numerically. Exploration of large datasets, display of simulation results and interactive steering of computation all require data visualization in some way, shape or form.

For more than thirty years of systems development, the software crisis has posed a problem. Generally, systems development surpasses budgets and time limits and is not reliable. Worse still, it doesn't satisfy users' requirements.

Java was designed to have all of the best features of existing languages. However, Java has no concept of asynchronous behavior. This is the main reason the threading mechanism is so important and that concurrent programming techniques are evolving quickly to the point where known patterns, whose behaviors are well understood, will become an integral part of the common Java environment.

Design Patterns are blueprints that describe how to design class structures and object interactions to solve commonly encountered problems. A Design Pattern can be as simple as the practice of using an interface to achieve polymorphism and as complicated as designs used to solve intricate concurrency problems.

Decisions The choice of encryption technologies is not always easy, but fortunately there are often several equally good options. The first step in choosing an algorithm is knowing the purpose to which it will be applied. Is it to ensure privacy, integrity, authenticity or to provide non-repudiation? Will it be used on a small amount of data or files so large that the encryption process could result in an unacceptable processing delay? The strength of an encryption method is dependent upon both the algorithm and the key length and can be understood in terms of the computational resources required to break it. The longer the key, the stronger any given algorithm. It is the value of the data and the length of time it must be protected that determines the necessary encryption strength. As long as the value of the data is lower than the cost of breaking the encryption, it is adequately protected.

The emergence of the Internet and other distributed networks puts increasing importance on the ability to create global software - that is, software that can be developed independently of the countries or languages of intended users and then translated for multiple countries or regions. Javaª 1.1 takes a major step forward in creating global applications and applets. It provides frameworks based on the Unicodeª 2.0 character set - the standard for international text - and an architecture for developing global applications, which can present messages, numbers, dates and currency in any country's conventional formats.

Sun's vision of network computing is a day when a constant, seamless, global connection - the Webtone -- is accessible anywhere at any time from any device (from smartcards to supercomputers). To realize this vision, Sun provides the Webtone foundation, enabling customers to securely develop for, deploy across and manage global corporate networks.

The process of designing reusable object-oriented software is one of the hardest problems faced by object-oriented software designers. This is mainly due to the fact that different software architectures have different requirements. However, design patterns give the software designer the ability to reuse some successful designs that have been used in other projects and have proved to be successful. Thus, design patterns help software designers design successful new software by using prior successful designs as a basis for their new design.

It seems that there is an increasing demand for Internet based applications. Every time I turn on my television, I see Internet-related advertisements or commercials ending with "See us on the Web at: http:// www.somebigco mpany.com'." These URLs actually refer to other computers out there in cyberspace. Each of these computers has one or more socket-based Web Servers administering connections, file transfers and other various duties. As the Internet begins to play a greater role in commerce, the demand for Web Servers or customized Web servlets will grow.

Java programmers are network programmers and increasingly, network programmers write applications that need encryption technology. The Internet is like a huge chat room. Not only is it a worldwide sniffable net, it's developing its own unique business infrastructure. New virtual services are required to provide the confidence in business transactions that has been available through a paper-based system. In addition to privacy, Internet commerce demands digital forms of signature, currency, notarization, purchase orders and receipts. Many of the most important Internet applications can be created only with the support of sophisticated cryptographical techniques. One of the great things about using Java is that it potentially allows the developer control over both the client and the server. New crypto classes will allow creation of applets that can provide security services within existing browsers.

The emergence of the Internet and other distributed networks puts increasing importance on the ability to create global software - that is, software that can be developed independently of the countries or languages of intended users and then translated for multiple countries or regions. Javaª1.1 takes a major step forward in creating global applications and applets. It provides frameworks based on the Unicodeª 2.0 character set - the standard for international text - and an architecture for developing global applications, which can present messages, numbers, dates and currency in any country's conventional formats.

Automated testing is essential to guaranteeing quality in Java applications with complex GUIs. Examination of newly available test tools and harnesses illuminates the manner in which strategic choices regarding testing need to be related to the nature of the software being tested.

In JDK 1.1, no other new feature is likely to have more impact on Java programmers than the less-publicized inner classes feature. It'll change the way in which Java programs have been traditionally written. The primary goal of this feature is to provide the ability to declare classes within classes.

Java's support for concurrency is sufficient enough to achieve a wide range of desired results. While the primitives provided are very powerful, they can also be easily misused and may lead to unpredictable behavior. It is well known that in a multithreaded environment, due to the lack of mature tools available, the debugging process could easily modify the state of the program being debugged.

Last month, I introduced the terms types, variables, classes, objects and references. If you understood the examples and correctly answered the test question I provided at the end of the article, you're well on your way to mastering the essential concepts that govern how all Java programs work. If you missed the article, look for it on SYS-CON's Web site at http://www.JavaDe velopersJournal.com. This month, I'm going to concentrate on eight tenets of Java programming. These tenetsare the "truths" that will guide you safely through the darkest complexities of Java syntax as it relates to assignments, casting, constants and method parameters.

The Internet has been very popular in the past few years. With its popularity still growing, increased demand for Internet network software has grown as well. One of the greatest advantages to developing Internet software with Java is in its robust networking support built into the core language. The java.net package provides us with classes representing URLs, URL connections and sockets. Combined with the java.io package, we can quite easily write sophisticated platform-independent networking (Internet) applications.

What JavaPlan Delivers The Java language and Java applets have taken the Internet by storm, yielding interactivity on Web pages in ways previously never seen. To date, however, Java has not been applied to larger scale development problems, a result of a concentration of effort on Java front-ends, but little by way of back ends. A new acquisition from Sun Microsystems is setting out to change that.

The evolution of Java has been truly mind-boggling, and quite unlike anything we have ever seen before in the computing domain. Seldom does a day go by without yet another software vendor pledging allegiance to the Java paradigm. Today, few among us will question the power and flexibility of Java. Still, one may ask, "Can Java, by itself, meet all our needs?" The answer to that question was given indirectly by the designers of the language itself when they made allowances for extending the reach of Java through a standard interface utilizing native methods.

Java is a programming language. Nothing complicated so far. And just like all other computer languages, it will not make a bad programmer into a good programmer. All the same techniques picked up while coding in, say, C or C++, generally can be applied to the same program in Java. But what happens if you're not coming from an experienced coding background. You don't have this wealth of knowledge. Fortunately or unfortunately, depending on your side of the fence, when it comes to coding multimedia applets many experienced developers are back at square one with the novices. The problem is that in pre-Web days, the majority of programmers never needed to worry about image manipulation procedures. But now, it would be rare for a Java programmer not to have coded some sort of image processing applet. Whether it is displaying a logo or animating a series of images, the problems that can occur are the same. Granted, unlike many other languages, Java makes displaying images very easy, however, without careful consideration, the resulting applet / application may look far from professional.

Why Test Applets? Why do we test an applet? What are we trying to show when we test? This article is addressed to the developer/tester, someone who is testing their own Applets. Nonetheless, all but a very few of the observations and techniques apply to the problem of testing someone else's code. The largest difference is probably the emotion upon finding a bug.

"Variables have types, objects have classes." This phrase, borrowed from the Java Language Specification, succinctly answers several questions that, judging by the frequency of their appearance in the Java news groups, are a common source of confusion for many Java programmers. It reinforces that variables and objects are different things and helps explain why "casts" are necessary, why Java "constants" can appear to be modifiable and what it really means for an argument to be passed to a method "by value". This month, I'll begin with some background information that will help those who are not yet comfortable with the terms types, variables, objects, classes and references to get up to speed. Then, I'll present a problem, based upon the exam questions for Sun's Java Certification Program, that will test your understanding of references and objects.

Introduction Java developers are constantly becoming frustrated because of unexpected encounters with Java security features. For example, a recent posting on comp.langs.java.security complained about difficulties in being able to open a network socket with Java. After reading the security introduction in the last issue of JDJ, it should be clear that allowing Web content to open arbitrary network connections on a workstation is highly undesirable. Not only could this circumvent existing security mechanisms, such as firewalls and IP address-based access control, but these network connections would appear to be initiated by the user, which could be embarrassing. Java applets are deliberately limited in their capability in order to protect users. Without these limitations, or some other protective mechanism, they would not be acceptable to corporate users.