Java is an important new programming language, designed by a team at Sun Microsystems. Many of you will have heard of it in the context of the Internet, which is where it made its initial impact. Sun started developing Oak, the forerunner of Java, in 1990. Java was released in 1993 and has grown from nothing to become widely accepted as one of the world's most important programming languages. All major web browsers now support Java and companies such as Microsoft and Apple are already building support into their operating systems. Many of the new Network Computers will run little other than Java programs.

At present, Java is usually thought of as a means of embedding fancy graphics or interaction into web pages. However, it is capable of much more than this. In fact, it is a language comparable to any other: Fortran, C, C++, Pascal or Modula-3. It provides all of the standard language constructs that you would expect and a standard library which goes beyond what any of these provides. It is available on most systems: Windows, Macintosh, Solaris, Linux and many others, including almost all varieties of UNIX.

As you will see later in this book, Java is capable of matrix manipulation, RSA encryption, computing pi and all of the other types of computation that a scientific programmer might want to perform.

• Java is totally platform independent. Your code will compile literally unchanged on any system. In addition the compiled code itself will run on any system. Even languages such as Pascal or C do not provide this degree of portability; in these languages the amount of accuracy that numerical data types store varies and certain pieces of behaviour do not have a defined standard. You will be able to switch systems or share code with colleagues much more easily.
• The Java standard libraries provide support for graphics. This is not true of any other popular language. It means that even graphical code is portable between systems, whereas under other systems it usually needs complete rewriting.
• The Java standard libraries provide arbitrary precision arithmetic in both integers and decimals. This is not true for any of the languages that we have mentioned.
• Java is a modern language. Its many technical virtues range from being object oriented to being multi-threaded, from being dynamic to being architecture neutral and cover many other buzzwords. This may not mean much to you; in practice it means that Java provides features that are much more powerful than older languages such as Pascal or C, and, since it was designed as a coherent whole, there are fewer strange side effects than in C++. As a simple example, in any of these three languages, if you allocate memory then you must keep track of it and deallocate it. In Java the memory is automatically tracked and deallocated when you have finished with it. Features like this make it harder to write buggy code.
• Java code run over the Internet is secure. Java is designed so that programs embedded in web pages can only have limited access to your computer. For example, they cannot read or write to the hard disk and cannot access memory allocated to different programs. When running Java code inside a web browser, you are protected from any malicious actions that it may try to perform. The only other technology for embedding programs into web pages, Microsoft's ActiveX, makes no attempt to provide any security at all. This security and its platform independence makes Java the standard for programs on the web. Simultaneously, the need for security does not cripple the Java language: programs that you have explicitly downloaded onto your local system or are writing yourself are as powerful (and potentially as risky) as any other form of program.
• Java is free. This is almost true of C/C++ where any UNIX machine will come with a compiler. However, at present Sun are providing their JDK (Java Development Kit) free of charge for Window 98/NT and Solaris and free ports exist to many other platforms. The website accompanying this book, at http://www.jscieng.co.uk/, provides pointers to Sun's versions for Windows and Solaris as well as to third-party ports of this software to other platforms. Of course, other companies such as SuperCede, Borland, Metrowerks, Microsoft and Symantec have also written their own competing compilers, some with nicer graphical user interfaces. You can pay and get a fuller service if you want to, but the JDK defines the standard.
• With most of the computer industry backing it, we can expect further exciting developments over the next few years.

In addition, if you are involved in any kind of teaching then Java provides two further benefits.

• Java code can be run in a web browser over the Internet, allowing you to write demonstration programs which your students will be able to run at any connected computer.
• From a student's point of view, knowledge of Java is a very marketable skill. Many courses include computer projects, usually performed in a language such as Pascal. By doing such projects in Java, the student loses nothing, since the basic syntax is as easy to learn, but gains all of the advantages listed above, such as better standard library support. In addition, the student gains experience with a language which is actually used in the computer industry.

In addition, unlike other Java books, our examples perform the kind of computations that a scientific programmer will be interested in. This book is not intended as a systematic source of good numerical algorithms - the programs are intended to illustrate language features. However, all of the examples perform a scientific computation of some sort and there are brief introductions to more serious numerical algorithms, software engineering and physical modelling in the second part of the book. These introductions are directed towards students who have not encountered these subjects before. We also include a description of Visual Numerics' `JNL, a Numerical Library for Java' and a simple library of our own, `JSGL, a Scientific Graphics Library for Java', to handle graphical output for you so that you do not need to learn the full structure of Java graphics. Both of these libraries are intended for professional numerical work. The JSGL will run on all platforms that support Java, in contrast to most other graphical systems and languages in which you must rewrite your code to switch platforms.

This book has a fast track for those who already know C/C++, which are superficially similar, and also a more elementary introduction for students who have done no previous computing. Whichever category you are in, I have tried to provide an easier introduction to the subject than many other books on Java. No knowledge of any particular programming language is assumed, nor is any familiarity with object orientation.