L09 Abstract

8/10/2019 L09 Abstract

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Programming Languages

Abstract Data Types and

Design Issues


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Outline

The Concept of Abstraction Introduction to Data AbstractionDesign IssuesLanguage Examples


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Abstraction

Two types of abstractions:Process abstraction: subprogramsData abstraction

Floatingpoint data type as data abstractionThe programming language will pro!ide "#$ a

way of creating !ariables of the %oatingpointdata type& and "'$ a set of operators formanipulating !ariables

Abstract away and hide the information of howthe %oatingpoint number is presented andstored


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Abstraction Data Type

Abstract data type: a userde(ned data typeDeclaration of the type and protocol of

operations on ob)ects of the type& i*e*& type+s

interface& are de(ned in a syntactic unit,interface indep* of implementation

-epresentation of ob)ects of the type is hiddenfrom program units that use these ob)ects, onlypossible operations are those pro!ided in type.s

de(nitionclass data type int

ob)ect !ariable i& )& /

method operators 0& & 1& 2

y 3 stac/#*top"$04, !s y 3 "x$ 0 4,


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Advantages of Data Abstraction

Ad!antage of ha!ing interfaceindependent of ob)ect representation orimplementation of operations:

5rogram organi6ation& modi(abilityAd!antage of 'nd condition "info* hiding$-eliability: 7y hiding data representations& user

code cannot directly access ob)ects of the type

or depend on the representation& allowing therepresentation to be changed without a8ectinguser code


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cont.....

Design Issues and Language Examples


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Language Requirements for ADTs

A syntactic unit to encapsulate type de(nitionA method of ma/ing type names and

subprogram headers !isible to clients& while

hiding actual de(nitions9ome primiti!e operations that are built into

the language processorExample: an abstract data type for stac/

create"stac/$& destroy"stac/$& empty"stac/$&push"stac/& element$& pop"stac/$& top"stac/$

9tac/ may be implemented with array& lin/edlist& ***


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Abstract Data Types in C++

The classis the encapsulation de!iceAll of the class instances of a class share a single

copy of the member functionsEach instance has own copy of class data membersInstances can be static& stac/ dynamic& heap

dynamic

Information hidingPrivateclause for hidden entitiesPublicclause for interface entitiesProtectedclause for inheritance


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ember !unctions Defined in Class

class Stack {private:

int *stackPtr, maxLen, topPtr;public:

Stack() { // a constructorstackPtr = new int !""#;maxLen = $$; topPtr = %!; &;

'Stack () {elete # stackPtr;&;voi pus (int num) {&;

voi pop () {&;int top () {&;int empt+ () {&;

&


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Language "#amples$ C++ %cont.&

Constructors:Functions to initiali6e the data members of

instances "they do not create the ob)ects$

ay also allocate storage if part of the ob)ectis heapdynamicImplicitly called when an instance is createdCan be explicitly called

;ame is the same as the class name


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Language "#amples$ C++ %cont.&

DestructorsFunctions to clean up after an instance is

destroyed, usually )ust to reclaim heap storage

Implicitly called when the ob)ect+s lifetimeendsCan be explicitly called;ame is the class name& preceded by a tilde

"


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'ses of t(e )tac* Class

voi main()

{

int topne;

Stack stk; //create an instance o-te Stack class

stk.pus(0); // c.-., stk 1= 0

stk.pus(!2);

topne = stk.top(); // c.-., 3stkstk.pop();

...

&


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Abstract Data Types in ava

9imilar to C00& except:All userde(ned types are classesAll ob)ects are allocated from the heap and

accessed through reference !ariablesethods must be de(ned completely in a classIndi!idual entities in classes ha!e access

control modi(ers "pri!ate or public$& ratherthan clauses

;o destructor implicit garbage collection


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An "#ample in ava

class Stack4lass {

private int # stack5e-;

private int maxLen, top6nex;

public Stack4lass() { // a constructorstack5e- = new int !""#;

maxLen = $$; topPtr = %!;&;

public voi pus (int num) {&;

public voi pop () {&;public int top () {&;

public boolean empt+ () {&;

&


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An "#ample in ava

public class 7stStack {

public static voi main(Strin8# ar8s) {

Stack4lass m+Stack = new Stack4lass();

m+Stack.pus(0);m+Stack.pus(0$);

S+stem.out.println(9:91m+Stack.top());

m+Stack.pop();

m+Stack.empt+();&

&

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L09 Abstract