Object model in Java: elements and application

Abstract

The Java programming language is a new object-oriented programming language that is gaining widespread popularity in the computer software industry because of its ease of learning, simplicity, generality, portability and networking capabilities. In this article, we discuss the semantic implementation in Java of each of the elements of the object model, identified by Booch [G. Booch, Object-Oriented Analysis and Design with Applications, 2nd Edition, Addison-Wesley, 1994], in addition to the mobility element. We show that Java, unlike other object-oriented languages, covers and simplifies all elements of the object model. An example illustrating those elements in Java will be drawn from a telecom software application.

Introduction

Java is a relatively new general purpose programming language introduced in 1996 by Sun Microsystems [2]. Java is object-oriented, portable, multithreaded, secure and easy to learn language. Being completely portable, a Java executable program can be run on various computer platforms without any modifications. A Java applet is a Java program that can be referred to in a hypertext-based web page. Then, once downloaded to a client web site, it is interpreted by the Java interpreter embedded in the client internet browser like Netscape and Microsoft's Internet Explorer.

The object-oriented programming paradigms is theoretically founded on the object model. A typical object-oriented software system implementation is centred around the dynamic creation, manipulation, storing and releasing of objects. Prior to the implementation, object-oriented analysis and design deal basically with the identification of the necessary objects and their interrelationships.

Many object-oriented languages have been introduced in the past, however none of them was fully object-oriented. A full-fledged object-oriented language is the one that addresses all the elements of the object model. Seven of these elements were identified by Booch [1] and are divided into major and minor elements. The major elements are: abstraction, modularity, encapsulation and hierarchy, and the minor elements are typing, concurrency and persistence. The study and comparison of object-oriented programming languages can be performed according to their implementations of the object model elements to which we added the object mobility as a minor element (cf. Fig. 1).

In this article, we study Java from the object model point of view. We also show, using an application example, the use of each concept of Java's object model elements. We will try, as much as possible, to describe the concepts of the object model using the Unified Modelling Language (UML) [3], an emerging internationally recognised standard for the specification and design modelling of object-oriented systems.

The rest of the article is organised as follows. Section 2 discusses each of the elements of the object model and their implementations in Java. Section 3 summarises the object model elements and compares three popular object-oriented languages with respect to that model. Section 4 illustrates the use of Java in telecom software engineering by considering a simple application example. Finally, Section 5 concludes the article and outlines some issues for future research.