1. Introduction

This work discusses the following two aspects of Java: (1) the implications of Java's lack of templates/generics and multiple inheritance of classes on software construction, and techniques to mitigate its effect; and (2) the influence of design patterns work on Java language and its APIs. Design patterns are a description of communicating objects and classes that are customized to solve a general design problem in a particular context [17,5,34]. Design patterns consolidate design experience that can potentially be reused in tackling a variety of problems, and in organizing and analyzing potential solutions to the problem. Many of these patterns improve software reuse and facilitate code evolution. Furthermore, the catalog of design patterns provides a rich vocabulary for documenting and sharing design decisions.

Idioms, on the other hand, are low-level ``patterns'' that describe how to solve implementation-specific problems in a programming language. Idioms demonstrate competent use of programming language features [5].

Java does not support generics and multiple inheritance of classes, thereby simplifying the language and its implementation. Section  reviews problems associated with support for multiple inheritance in existing object-oriented languages. Sections and analyze idiomatic approximations to these features in Java using only single inheritance of classes and multiple inheritance of interfaces. Section  presents Java APIs from patterns perspective. In particular, design patterns embodied by various packages in Java are documented so as to enable using existing literature on patterns to elucidate the pros and the cons of the design decisions. This section is intentionally brief and defers details to the seminal work of [17] and the recent independent work of [11,13,19]. A lot of related material is also available on-line starting at the URL http://www.objenv.com/cetus/software.html among others.

In other words, this paper explores:

• Patterns used by the designers of Java / Java APIs. In fact, Java / Java APIs are a concrete embodiment of several design patterns, and these ``reverse engineered'' patterns shed light on the consequences of the design decisions.

• Patterns supported by Java APIs to facilitate software reuse by Java programmers. The rationale behind the design of some of the built-in Java classes is provided to better appreciate the ``primitives'' at programmers' disposal.

• Idioms used by programmers to approximate multiple inheritance and generics, which are not directly supported by Java.

The overall objective of this paper is to consolidate a software engineering perspective on the Java language and the accompanying libraries. This comprehensive overview of Java underscores the fact that Java designers have included only tried and time-tested ideas in the language. The latter part of the paper complements prior work on the general theme of ``Design Patterns and Java'' described in [11,13,23,19,14,16], etc.