C# 0 The Complete Reference

Controlling Access: A Case Study

To better understand the “how and why” behind access control, a case study is useful. One 

of the quintessential examples of object-oriented programming is a class that implements a 

stack. As you probably know, a 

stack

 is a data structure that implements a last-in, first-out 

list. Its name comes from the analogy of a stack of plates on a table. The first plate on the 

table is the last one to be used.

A stack is a classic example of object-oriented programming because it combines storage 

for information along with the methods that access that information. Thus, a stack is a 

data

engine

 that enforces the last-in, first-out usage. Such a combination is an excellent choice for 

a class in which the members that provide storage for the stack are private, and public methods 

provide access. By encapsulating the underlying storage, it is not possible for code that uses 

the stack to access the elements out of order.

A stack defines two basic operations: 

push

 and 

pop.

 A push puts a value onto the top of 

the stack. A pop removes a value from the top of the stack. Thus, a pop is consumptive; once 

a value has been popped off the stack, it has been removed and cannot be accessed again.

The example shown here creates a class called 

Stack

 that implements a stack. The 

underlying storage for the stack is provided by a private array. The push and pop operations 

are available through the public methods of the