Ka-chun Chan CIS24 SA 3/30/03 Project #2 Prof. Kopec Object-Oriented Programming - Java On May 23, 1995, John Gage, director of the Science Office for Sun Microsystems, and Marc Andreessen, cofounder and Executive vice President at NetscapeTM, stepped onto a stage and announced to the SunWorldTM audience that JavaTM technology was real, it was official, and it was going to be incorporated into Netscape NavigatorTM, the world's portal to the Internet. The JavaTM platform is based on the power of networks and the idea that the same software should run on many different kinds of computers, consumer gadgets, and other devices. Since its initial commercial release in 1995, Java technology has grown in popularity and usage because of its true portability. The Java platform allows you to run the same Java application on lots of different kinds of computers. There have eleven buzzwords that explain its design goals and accomplishments: ¾ Simple ¾ Object Oriented ¾ Distributed 1¾ Robust ¾ Secure ¾ Architecture ¾ Portable ¾ Interpreted ¾ High Performance ¾ Multithreaded ¾ Dynamic Java is a simple language. The Java designers were trying to create a language that a programmer could learn quickly, so the number of language constructs has been kept relatively small. It is an object-oriented programming language. As a programmer, this means that you focus on the data in your application and methods that manipulate that data, rather than thinking strictly in terms of procedures. A distributed language means that it provides a lot of high-level support for networking. It 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. Java technology 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 technology lets you construct applications that can't be invaded from outside. In the network environment, applications written in the Java programming 2language are secure from intrusion by unauthorized code attempting to get behind the scenes and create viruses or invade file systems. Because Java programs are compiled to an architecture neutral byte-code format, a Java application can run on any system, as long as that system implements the Java Virtual Machine. Architecture neutrality is just one part of a truly portable system. But Java goes even further, by making sure that there are no “implementation-dependent” aspects of the language specification. The Java interpreter can execute Java byte-codes directly on any machine to which the interpreter and run-time system have been ported. In an interpreted platform such as Java technology-based system, the link phase of a program is simple, incremental, and lightweight. If you use an interpreter to execute the byte-codes, “high performance” is not the term that we would use. However, on many platforms, there is also another form of compilation, the just-in-time (JIT) compilers. These work by compiling the byte-codes into native code once, caching the results, and then calling them again if needed. This approach speeds up commonly used code. Java is a multithreaded language; it provides support for multiple threads of execution that can handle different tasks. An important benefit of 34multithreading is that it improves the interactive performance of graphical applications for the user. 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. public class HelloWorld { public static void main(String[] args) { System.out.println("Hello world!"); } } Reference: Cay S. Horstmann & Gary Cornell, “Core Java 2”, Sun Microsystems David Flanagan, “Java in a nutshell”, O’Reilly Java.sun.com, http://java.sun.com/ Copyright @ 1995-2003 Sun Microsystems,