ADT - CMPS 101 Algorithms and Abstract Data Types ADTs and...

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1 CMPS 101 Algorithms and Abstract Data Types ADTs and Modules in Java and ANSI C Introduction This document introduces the concepts of Modules and ADTs, and describes how to implement them in both Java and ANSI C. Informally, an Abstract Data Type (ADT) is a collection of mathematical objects of some kind, together with some associated operations on those objects. When an ADT is used in a program, it is usually implemented in its own module . A module is a self-contained component of a program having a well defined interface that details its role and relationship to the rest of the program. Why are ADTs necessary? The standard data types provided by many programming languages are not powerful enough to capture the way we think about the higher level objects in our programs. This is why most languages have a type declaration mechanism the allows the user to create high level types as desired. Often the implementation of these high level types gets spread throughout the program, creating complexity and confusion. Errors may occur when the legal operations on the high level types are not well defined or are not consistently used. The term Abstract Data Type can mean different things to different people, but for the purposes of this course, an ADT consists of two things: (1) A set S of “mathematical structures”, the elements of which are called states . (2) An associated set of operations which can be applied to the states in S . Each ADT instance or object has a current state which is one of the elements of the set S . The operations on S fall (roughly) into two classes. Manipulation procedures are operations which cause an ADT instance to change it's state. Access functions are operations which return information about an ADT instance, without altering it's state. In this course we will maintain a clear distinction between the two types of operations. We will also from time to time consider operations which don't fall into either category, but we will not use operations which belong to both categories. An ADT is an abstract mathematical entity which exists apart from any program or computing device. On the other hand, ADTs are frequently implemented by a program module. We will distinguish between the mathematical ADT and it's implementation in a programming language. In fact, a single ADT could have many different implementations, all with various advantages and disadvantages. Example Consider an integer queue . In this case S is the set of all finite sequences of integers, and the associated operations are: Enqueue, Dequeue, getFront, getLength, and isEmpty. The meanings of these operations are given below. One possible state for this ADT is (5, 1, -7, 2, -3, 4, 2). (It is recommended that the reader who is unfamiliar with elementary data structures such as queues, stacks, and lists, review sections 10.1 and 10.2 of the text.)
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2 Manipulation procedures Enqueue Insert a new integer at the back of the queue Dequeue Remove an integer from the front of the queue
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This note was uploaded on 12/03/2009 for the course CS CS101 taught by Professor Agoreback during the Spring '09 term at American College of Gastroenterology.

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ADT - CMPS 101 Algorithms and Abstract Data Types ADTs and...

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