3.3 Programming Environment

What programming environment should be used to implement this system? We needed object oriented programming, a suitable support for network communication and appropriate functionalities to create graphical user interfaces.

• C++: C and C++ are one of the most commonly used programming languages today. That is especially the case for Unix platforms. Since our system had to run at least be available for Unix and Win32 platforms we would have had to develop two versions -- one for Unix with X11/Motif support and the other with Visual C++ for Win32 systems.

• Web based approach: It is easy to create a common platform for many remote users with this method. HTML pages are usually enhanced by CGI scripts, Javascripts and Java applets to improve the interactivity of web pages. A structured way to create bigger systems is however not recommended with that approach. It is also almost impossible to use the advantages of object oriented programming. The idea of using web pages was soon dismissed.

• Java: Java is an upcoming programming language that is especially designed to create system independent and network close applications.

It was decided that the project should be developed with Java. We used Java Development Kid version 1.1.5 to implement all parts of the project. There were several advantages that suggested the use of Java:

• Platform independence: Java can be considered a compiler and interpreter. The source code is first translated into the so-called `Java Bytecode' by the Java Compiler. That bytecode is finally interpreted by a Java Virtual Machine (Java VM). This virtual machine is available for a broad number of architectures. This makes a Java program highly platform independent because the bytecode can be executed on every machine for which a Java VM exists.

• User interaction: Java is in most cases a better approach for real-time services compared to a web-server with CGI Scripts. Parts of the code can be executed on the client's machine. This allows quicker responses to user requests, since not every single user action has to be transferred to the server. The problem of the stateless behavior of web-servers is also not present with Java. Additionally, an operation that effects only the local user can be executed locally and doesn't need to burden the server.

• Object serialization: Java provides object serialization that can be used to store, reload and transport objects across different platforms. Those operations are actually streams, which could be files or further Java processes. An object usually has links to other objects, which might contain links to further objects and so on. If an object is exported, then all its referenced companions have to be stored also. Problems can occur if objects are connected in a circular path. Object serialization is a method to export objects in a serialized manner. First, the objects member variables are exported. This is repeated for all linked objects except for already exported objects. Object serialization also takes care of the representation of basic data types. It performs all necessary conversions for different system architectures. For example conversions between big endian and little endian.

• Remote Method Invocation (RMI): RMI is a mechanism comparable to remote procedure calls in C. It allows the execution of object methods that are members of remote objects. Remote objects reside on another Java process, which can run anywhere on the network. For example a client (which is an object) can call methods of the server and vice versa. The transport of method arguments (which are objects too) is done by object serialization.

Of course, there are also disadvantages of Java:

• Execution speed: The execution speed of Java programs is usually lower compared to programs developed with compiler languages like C++. The fact that the bytecode has to be interpreted is the reason for slower execution. However, there are special compilers available for some platforms, which translate the bytecode into pure machine code. These applications are almost as fast as programs designed with usual compiler languages.

• Short live time of Java versions: Java is a relatively young programming language. Sun Microsystems is constantly improving the language (actually its supporting packages) and its functionality. The periods between new versions of the language are very short. JDK version 1.1.5 was the newest version while this project was started. While working on this project, a number of updates and a completely revised version (JDK 1.2) was released. Unfortunately, programs written in different versions of Java are not necessarily executable on the same virtual machine. This leads to the prediction, that software written in Java will need to be updated in the near future.

It was decided that the advantages of Java overcome the disadvantages. Since platform independence was a major goal of our project, it became clear that other languages could not achieve the desired grade of platform independence as Java does.

Hopefully, Java will not fall to the same fate as Unix did and lose its main advantage, the platform independence. This would be the case if major software companies start to develop and sell their own, not compatible Java versions. We can hope that developers avoid using incompatible Java derivatives like Microsoft's Visual J++.