CSC/ECE 517 Fall 2011/ch1 2b qu

Access Control in o-o Languages

O-o languages have different approaches to controlling access to variables and methods. Ruby, for example, doesn't allow an object to access the private features of another object, even if the other object is an instance of the same class. Java 1.0 had a "private protected" access specifier that allowed subclasses to access a variable, but not non-subclasses in the same package. It was dropped, probably because it was confusing. Have philosophies about allowing access become more restrictive over the years, as accessor methods have become more prominent?

Introduction

Access control is a feature that is available in many programming languages that allows the programmer to define a set of rules that govern how the elements in a program (for example methods or attributes in a class) can be used from different contexts. While some programming languages like C++, JAVA etc have predefined policies for access control (public/protected/private) allowing structured but limited power in the hands of the programmer, others such as Eiffel provide more flexible access control scheme (selective export). Here, we will look at access control policies of some object-oriented programming languages and how these policies have changed over the years.