Mark Evered

Genja-a new proposal for parameterised types in Java

Recent proposals for adding parameterised types to Java have left a number of important practical issues undiscussed. We present the language Genja which is a novel generic extension of Java oriented towards practical support for generic collection types. We discuss design alternatives related to extending the power of unconstrained genericity, solving the weaknesses of constrained genericity in other proposals and defining the compatibility of named and anonymous instantiations. By enhancing support for reusability and providing a higher level style of programming via a library of standard generic collection types, Genja aims to extend Javas contribution to efficient software production.

How Well Do Inheritance Mechanisms Support Inheritance Concepts

Inheritance mechanisms are used to express many different programming concepts. In this paper we analyse these inheritance concepts to determine the requirements for an inheritance mechanism which is to support the concepts well. On the basis of this analysis we identify weaknesses in current mechanisms, particularly in the areas of modelling and signature modification and show how an inheritance mechanism can better fulfil the requirements while remaining type-safe.

Statically Qualified Types in Timor

In earlier papers qualifying types were presented as a technique for dynamically qualifying objects in a general way. This paper considers how such types can be composed statically into the definitions of other types.

Collection types and implementations in object-oriented software libraries

Collection classes are ideal candidates for software reuse and therefore have an important role in the development and use of object-oriented class libraries. We analyze representative collection libraries, pointing out the main problems from the viewpoint of their practical usability in programs. We then identify a small number of independent concepts relevant to the design of libraries of collections and show how an orthogonal treatment of these concepts can solve the problems identified. Because existing object-oriented languages, even newer ones, do not completely support all the relevant concepts (although most of the critical points are well-known), we show to what extent it would be possible to realize our proposals, and what remains as a challenge in the design of future languages.

A Flexible Object Invocation Language Based on Object-Oriented Language Definition

The objects accessible by a user at a particular time in an object-oriented system form a working environment. The invocation language via which this environment is viewed and manipulated can be regarded as semantically flexible since the set of operations available to the user is the union of the methods of all currently visible classes. In this paper we present a language system in which class definitions are extended to include appropriate syntax rules for the methods and which is consequently also syntactically flexible. The requirements for such a system both from the point of view of a user and with regard to efficient implementation are discussed. An implementation of such a flexible invocation language within a persistent object-based operating system is then presented.

Object-oriented Access Control in Jarrah.

Given the sensitivity of the data stored in many information systems and the use of networks to support distributed applications, it is increasingly important to enable precise control of who can access the data in what way. Standard per-method access control lists are not sufficient to capture the complexity of the access constraints which arise if the concept of minimal access is taken seriously. In this paper we describe and justify the design of the access control aspect of the persistent object-oriented language Jarrah, a Java extension for programming secure distributed applications.

How can covariance in pragmatical class methods be made statically type-safe?

Binary class methods are often more suitable for modelling binary operations than binary instance methods. Allowing covariant parameter type adaptations in class methods can make them even more attractive. We discuss the implications of covariant class methods on type safety. We discuss two examples, one type-safe at run-time and the other not, and formulate type rules that make it possible to identify the difference at compile-time.

Eine Evaluierung des Java JDK 1.2 Collections Framework aus Sicht der Softwaretechnik

Sammlungen von Daten spielen eine wichtige Rolle bei fast jeder Art der Programmierung. Aus diesem Grunde bieten praktisch benutzte objektorientierte Sprachen Standard-Bibliotheken an, die Klassen fur die Verwaltung von Objektsammlungen enthalten. Diese Bibliotheken sind besonders dafur kritisiert worden, das sie softwaretechnische Prinzipien wie Geheimnisprinzip und Orthogonalitat nicht hinreichend berucksichtigen. In diesem Beitrag evaluieren wir das neue ‘Collections Framework‘ des ‘Java Development Kit‘ 1.2, das durch die Definition der ‘Core Collection Interfaces‘ einige Vorteile hinsichtlich der Verstandlichkeit und Erweiterbarkeit solcher Bibliotheken bietet. Wir diskutieren sowohl Schwachen des Framework, die auf einer inkonsequenten Anwendung von Softwaretechnikprinzipien beruhen, als auch Probleme, die aus der Definition der Sprache Java selbst resultieren.

Software engineering despite object-orientation

Object-oriented languages can potentially make a great contribution to enhancing software quality and supporting the software engineering process. Despite this potential, we contend that a number of central features of object-oriented languages are in fact contrary to well-known software engineering principles and goals and therefore represent a hindrance to software engineering rather than a contribution. In this paper we look at the class construct, inheritance, genericity and at object-oriented collection frameworks and suggest ways these could be modified to better supporting software engineering principles.