Introduction to Java

1.1 - Beginnings of the Java Language Project
1.2 - Design Goals of Java
1.3 - The Java Base System
1.4 - The Java Environment--a New Approach to Distributed Computing

The Next Stage of the Known,
Or a Completely New Paradigm?

Taiichi Sakaiya--The Knowledge-Value Revolution

The Software Developer's Burden

Imagine you're a software application developer. Your programming language of choice (or the language that's been foisted on you) is C or C++ . You've been at this for quite a while and your job doesn't seem to be getting any easier. These past few years you've seen the growth of multiple incompatible hardware architectures, each supporting multiple incompatible operating systems, with each platform operating with one or more incompatible graphical user interfaces. Now you're supposed to cope with all this and make your applications work in a distributed client-server environment. The growth of the Internet, the World-Wide Web, and "electronic commerce" have introduced new dimensions of complexity into the development process.

The tools you use to develop applications don't seem to help you much. You're still coping with the same old problems; the fashionable new object-oriented techniques seem to have added new problems without solving the old ones. You say to yourself and your friends, "There has to be a better way"!

The Better Way is Here Now

Now there is a better way--it's the Java€ programming language environment ("Java" for short) from Sun Microsystems. Imagine, if you will, this development world...

Your programming language is object oriented, yet it's still dead simple.
Your development cycle is much faster because Java is interpreted. The compile-link-load-test-crash-debug cycle is obsolete--now you just compile and run.
Your applications are portable across multiple platforms. Write your applications once, and you never need to port them--they will run without modification on multiple operating systems and hardware architectures.
Your applications are robust because the Java run-time system manages memory for you.
Your interactive graphical applications have high performance because multiple concurrent threads of activity in your application are supported by the multithreading built into Java environment.
Your applications are adaptable to changing environments because you can dynamically download code modules from anywhere on the network.
Your end users can trust that your applications are secure, even though they're downloading code from all over the Internet; the Java run-time system has built-in protection against viruses and tampering.

You don't need to dream about these features. They're here now. The Java Programming Language Environment provides a portable, interpreted, high-performance, simple, object-oriented programming language and supporting run-time environment. This introductory chapter provides you with a brief look at the main design goals of the Java system; the remainder of this paper examines the features of Java in more detail.

At the end of this paper you'll find a chapter that describes the HotJava€ Browser ("HotJava" for short). HotJava is an innovative World-Wide Web browser, and the first major applications written using the Java environment. HotJava is the first browser to dynamically download and execute Java code fragments from anywhere on the Internet, and to so so in a secure manner.

1.1 Beginnings of the Java Language Project

Java is designed to meet the challenges of application development in the context of heterogeneous, network-wide distributed environments. Paramount among these challenges is secure delivery of applications that consume the minimum of system resources, can run on any hardware and software platform, and can be extended dynamically.

Java originated as part of a research project to develop advanced software for a wide variety of networked devices and embedded systems. The goal was to develop a small, reliable, portable, distributed, real-time operating environment. When the project started, C++ was the language of choice. But over time the difficulties encountered with C++ grew to the point where the problems could best be addressed by creating an entirely new language environment. Design and architecture decisions drew from a variety of languages such as Eiffel, SmallTalk, Objective C, and Cedar/Mesa. The result is a language environment that has proven ideal for developing secure, distributed, network-based end-user applications in environments ranging from networked-embedded devices to the World-Wide Web and the desktop.

1.2 Design Goals of Java

The design requirements of Java are driven by the nature of the computing environments in which software must be deployed.

The massive growth of the Internet and the World-Wide Web leads us to a completely new way of looking at development and distribution of software. To live in the world of electronic commerce and distribution, Java must enable the development of secure, high performance, and highly robust applications on multiple platforms in heterogeneous, distributed networks.

Operating on multiple platforms in heterogeneous networks invalidates the traditional schemes of binary distribution, release, upgrade, patch, and so on. To survive in this jungle, Java must be architecture neutral, portable, and dynamically adaptable.

The Java system that emerged to meet these needs is simple, so it can be easily programmed by most developers; familiar, so that current developers can easily learn Java; object oriented, to take advantage of modern software development methodologies and to fit into distributed client-server applications; multithreaded, for high performance in applications that need to perform multiple concurrent activities, such as multimedia; and interpreted, for maximum portability and dynamic capabilities.

Together, the above requirements comprise quite a collection of buzzwords, so let's examine some of them and their respective benefits before going on.

1.2.1 Simple, Object Oriented, and Familiar

Primary characteristics of Java include a simple language that can be programmed without extensive programmer training while being attuned to current software practices. The fundamental concepts of Java are grasped quickly; programmers can be productive from the very beginning.

Java is designed to be object oriented from the ground up. Object technology has finally found its way into the programming mainstream after a gestation period of thirty years. The needs of distributed, client-server based systems coincide with the encapsulated, message-passing paradigms of object-based software. To function within increasingly complex, network-based environments, programming systems must adopt object-oriented concepts. Java provides a clean and efficient object-based development environment.

Programmers using Java can access existing libraries of tested objects that provide functionality ranging from basic data types through I/O and network interfaces to graphical user interface toolkits. These libraries can be extended to provide new behavior.

Even though C++ was rejected as an implementation language, keeping Java looking like C++ as far as possible results in Java being a familiar language, while removing the unnecessary complexities of C++. Having Java retain many of the object-oriented features and the "look and feel" of C++ means that programmers can migrate easily to Java and be productive quickly.

1.2.2 Robust and Secure

Java is designed for creating highly reliable software. It provides extensive compile-time checking, followed by a second level of run-time checking. Language features guide programmers towards reliable programming habits. The memory management model--no pointers or pointer arithmetic--eliminates entire classes of programming errors that bedevil C and C++ programmers. You can develop Java language code with confidence that the system will find many errors quickly and that major problems won't lay dormant until after your production code has shipped.

Java is designed to operate in distributed environments, which means that security is of paramount importance. With security features designed into the language and run-time system, Java lets you construct applications that can't be invaded from outside. In the networked environment, applications written in Java are secure from intrusion by unauthorized code attempting to get behind the scenes and create viruses or invade file systems.

1.2.3 Architecture Neutral and Portable

Java is designed to support applications that will be deployed into heterogeneous networked environments. In such environments, applications must be capable of executing on a variety of hardware architectures. Within this variety of hardware platforms, applications must execute atop a variety of operating systems and interoperate with multiple programming language interfaces. To accommodate the diversity of operating environments, the Java compiler generates bytecodes--an architecture neutral intermediate format designed to transport code efficiently to multiple hardware and software platforms. The interpreted nature of Java solves both the binary distribution problem and the version problem; the same Java language byte codes will run on any platform.

Architecture neutrality is just one part of a truly portable system. Java takes portability a stage further by being strict in its definition of the basic language. Java puts a stake in the ground and specifies the sizes of its basic data types and the behavior of its arithmetic operators. Your programs are the same on every platform--there are no data type incompatibilities across hardware and software architectures.

The architecture-neutral and portable language environment of Java is known as the Java Virtual Machine. It's the specification of an abstract machine for which Java language compilers can generate code. Specific implementations of the Java Virtual Machine for specific hardware and software platforms then provide the concrete realization of the virtual machine. The Java Virtual Machine is based primarily on the POSIX interface specification--an industry-standard definition of a portable system interface. Implementing the Java Virtual Machine on new architectures is a relatively straightforward task as long as the target platform meets basic requirements such as support for multithreading.

1.2.4 High Performance

Performance is always a consideration. Java achieves superior performance by adopting a scheme by which the interpreter can run at full speed without needing to check the run-time environment. The automatic garbage collector runs as a low-priority background thread, ensuring a high probability that memory is available when required, leading to better performance. Applications requiring large amounts of compute power can be designed such that compute-intensive sections can be rewritten in native machine code as required and interfaced with the Java environment. In general, users perceive that interactive applications respond quickly even though they're interpreted.

1.2.5 Interpreted, Threaded, and Dynamic

The Java interpreter can execute Java bytecodes directly on any machine to which the interpreter and run-time system have been ported. In an interpreted environment such as Java system, the link phase of a program is simple, incremental, and lightweight. You benefit from much faster development cycles--prototyping, experimentation, and rapid development are the normal case, versus the traditional heavyweight compile, link, and test cycles.

Modern network-based applications, such as the HotJava World-Wide Web browser, typically need to do several things at the same time. A user working with HotJava can run several animations concurrently while downloading an image and scrolling the page. Java's multithreading capability provides the means to build applications with many concurrent threads of activity. Multithreading thus results in a high degree of interactivity for the end user.

Java supports multithreading at the language level with the addition of sophisticated synchronization primitives: the language library provides the Thread class, and the run-time system provides monitor and condition lock primitives. At the library level, moreover, Java's high-level system libraries have been written to be thread safe: the functionality provided by the libraries is available without conflict to multiple concurrent threads of execution.

While the Java compiler is strict in its compile-time static checking, the language and run-time system are dynamic in their linking stages. Classes are linked only as needed. New code modules can be linked in on demand from a variety of sources, even from sources across a network. In the case of the HotJava browser and similar applications, interactive executable code can be loaded from anywhere, which enables transparent updating of applications. The result is on-line services that constantly evolve; they can remain innovative and fresh, draw more customers, and spur the growth of electronic commerce on the Internet.

1.3 The Java Base System

The complete Java system includes a number of libraries of utility classes and methods of use to developers in creating multi-platform applications. Very briefly, these libraries are:

java.lang--the collection of base types (language types) that are always imported into any given compilation unit. This where you'll find the declarations of Object (the root of the class hierarchy) and Class, plus threads, exceptions, wrappers for the primitive data types, and a variety of other fundamental classes.

java.io--streams and random-access files. This is where you find the rough equivalent of the Standard I/O Library you're familiar with on most UNIX systems. A further library is called java.net, and provides support for sockets, telnet interfaces, and URLs.

java.util--container and utility classes. Here you'll find classes such as Dictionary, HashTable, and Stack, among others, plus encoder and decoder techniques, and Date and Time classes.

java.awt--an Abstract Windowing Toolkit that provides an abstract layer enabling you to port Java applications easily from one window system to another. This library contains classes for basic interface components such as events, colors, fonts, and controls such as buttons and scrollbars.

1.4 The Java Environment--a New Approach to Distributed Computing

Taken individually, the characteristics discussed above can be found in a variety of software development environments. What's completely new is the manner in which Java and its run-time system have combined them to produce a flexible and powerful programming system.

Developing your applications using Java results in software that is portable across multiple machine architectures, operating systems, and graphical user interfaces, secure, and high performance. With Java, your job as a software developer is much easier--you focus your full attention on the end goal of shipping innovative products on time, based on the solid foundation of Java. The better way to develop software is here, now, brought to you by the Java language environment.

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