ICE1341 Programming Languages Spring 2005 Lecture #18 Lecture #18 In-Young Ko iko.AT. icu.ac.kr iko.AT. icu.ac.kr Information and Communications University

ICE1341 ICE1341 Programming LanguagesProgramming Languages

Spring 2005Spring 2005

Lecture #18Lecture #18

In-Young Koiko .AT. icu.ac.kr

Information and Communications University (ICU)

Spring 2005 2 ICE 1341 – Programming Languages © In-Young Ko, Information and Communications University

AnnouncementsAnnouncements

Makeup class: Makeup class: Wednesday May 18Wednesday May 18thth 4:00PM or 7:00PM4:00PM or 7:00PM????

Handling XML data in a Java programHandling XML data in a Java program W3C Document Object Model W3C Document Object Model ((www.w3.org/DOM/www.w3.org/DOM/))

A simple way to read an XML file in Java A simple way to read an XML file in Java ((www.developerfusion.com/show/2064/www.developerfusion.com/show/2064/))

Working with XML Working with XML ((java.sun.com/xml/jaxp/dist/1.0.1/docs/tutorial/index.htmljava.sun.com/xml/jaxp/dist/1.0.1/docs/tutorial/index.html))

These will be covered in details in the next These will be covered in details in the next classclass


DTD (Data Type Definitions)DTD (Data Type Definitions) Final Project AssignmentFinal Project Assignment Chapter 10 – Implementing SubprogramsChapter 10 – Implementing Subprograms

Activation RecordsActivation Records Implementing Subprograms with Stack-Implementing Subprograms with Stack-

Dynamic Local Variables (Dynamic chains)Dynamic Local Variables (Dynamic chains) Implementing Recursive SubprogramsImplementing Recursive Subprograms Implementing Nested Subprograms (Static Implementing Nested Subprograms (Static

chains, Reference to a variable)chains, Reference to a variable)

Last LectureLast Lecture


This LectureThis Lecture

Implementing SubprogramsImplementing Subprograms Implementing Program BlocksImplementing Program Blocks Implementing Dynamic ScopingImplementing Dynamic Scoping

Abstraction and EncapsulationAbstraction and Encapsulation Abstract Data TypesAbstract Data Types Encapsulation ConstructsEncapsulation Constructs Naming EncapsulationsNaming Encapsulations


Static Chains to Access VariablesStatic Chains to Access Variablesprogram program Main_2Main_2;; var X : integer;var X : integer; procedure procedure BigsubBigsub;; var A, B, C : integer;var A, B, C : integer; procedure procedure Sub1Sub1;; var A, D : integer;var A, D : integer; beginbegin A := B + C;A := B + C; end;end; procedure procedure Sub2Sub2(X : integer);(X : integer); var B, E : integer;var B, E : integer; procedure procedure Sub3Sub3;; var C, E : integer;var C, E : integer; beginbegin Sub1;Sub1; E := B + A:E := B + A: end;end; beginbegin Sub3;Sub3; A := D + E;A := D + E; end;end; beginbegin Sub2(7);Sub2(7); end;end; beginbegin Bigsub;Bigsub; end.end. Ada

References to References to the variable Athe variable A

(0, 3)(0, 3)

(2, 3)(2, 3)

(1, 3)(1, 3)


Evaluation of the Static Chain MethodEvaluation of the Static Chain Method

A nonlocal reference is A nonlocal reference is slowslow if the number of if the number of scopes between the reference and the scopes between the reference and the declaration of the referenced variable is largedeclaration of the referenced variable is large

Time-critical code is difficult, because the costs Time-critical code is difficult, because the costs of of nonlocal references are not equalnonlocal references are not equal, and can , and can change with code upgrades and fixeschange with code upgrades and fixes

DisplayDisplay: An alternative to static chains. An : An alternative to static chains. An array of static linksarray of static links ( (addresses of accessible addresses of accessible activation record instancesactivation record instances). ).


Program BlocksProgram Blocks

2. Allocate locals 2. Allocate locals on top of the on top of the activation activation record instancerecord instance Must use a Must use a

different different method to method to access localsaccess locals

void main () {void main () {int x, y, z;int x, y, z;while ( … ) {while ( … ) { int a, b, c;int a, b, c; … … while ( … ) {while ( … ) {

int d, e;int d, e; … …

}}}}while ( … ) {while ( … ) { int f, g;int f, g; … …}}……

}}

1. Treat blocks as 1. Treat blocks as parameterless subprogramsparameterless subprograms


Implementing Dynamic Scoping (1)Implementing Dynamic Scoping (1)

void sub3() {void sub3() {int int xx, , zz;;x = u + v;x = u + v;……

}}void sub2() {void sub2() {

int int ww, , xx;;……


int int vv, , ww;;……

}}void main() {void main() {

int int vv, , uu;;……

}}11

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Deep AccessDeep Access: Nonlocal : Nonlocal references are found by references are found by searching the activation searching the activation record instances on the record instances on the dynamic chaindynamic chain

Length of chainLength of chain cannot be statically cannot be statically determined at determined at compile timecompile time

Slower executionSlower execution Every activation Every activation

record instance must record instance must have have variable namesvariable names

* AW Lecture Notes


Implementing Dynamic Scoping (2)Implementing Dynamic Scoping (2)

void sub3() {void sub3() {int int xx, , zz;;x = u + v;x = u + v;……


int int ww, , xx;;……


int int vv, , ww;;……

}}Void main() {Void main() {

int int vv, , uu;;……

}}

Shallow AccessShallow Access One stack for eachOne stack for each variable name variable name

Central tableCentral table that has a that has a locationlocation and an and an ““active bitactive bit” for each different variable ” for each different variable name in a programname in a program

e.g., COBOLe.g., COBOL* AW Lecture Notes

11

22

44

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2

1

2

2

sub3

Spring 2005 10

ICE 1341 – Programming Languages © In-Young Ko, Information and Communications University

Chapter 11Chapter 11Abstraction and Abstraction and EncapsulationEncapsulation

Spring 2005 11


AbstractionAbstraction

Extraction of Extraction of essential characteristicsessential characteristics (data (data fields and functions) of an objectfields and functions) of an object

Not including unimportant details of an objectNot including unimportant details of an object

FriendFriend- name : String- name : String- email : String- email : String- phone: String- phone: String

<<constructor>><<constructor>> Friend(name: String) Friend(name: String)+ getName() : String+ getName() : String+ setName(name: String)+ setName(name: String)……

An abstraction of the real-world objectAn abstraction of the real-world object

Spring 2005 12


Abstraction Abstraction – cont.– cont.

AbstractionAbstraction: A view or representation of an : A view or representation of an entity that includes entity that includes only the attributes of only the attributes of significancesignificance in a particular context in a particular context Implementation details are hiddenImplementation details are hidden from users from users Simplify programming processSimplify programming process Types: Types: Data AbstractionData Abstraction, , Process AbstractionProcess Abstraction

StackStack

PushPush PopPop

TopTop

Data structureData structure – a list that grows and – a list that grows and shrinks at one end onlyshrinks at one end only

OperationsOperations – – push(stk1, ele), pop(stk1), push(stk1, ele), pop(stk1), top(stk1), create(stk1), destroy(stk1)top(stk1), create(stk1), destroy(stk1)

Spring 2005 13


Abstract Data TypesAbstract Data Types Abstract Data TypeAbstract Data Type: A user-defined data type : A user-defined data type

that satisfies the following two conditions:that satisfies the following two conditions: The The representationrepresentation of, and of, and operationsoperations on, on, objectsobjects of of

the type are defined in a the type are defined in a single syntactic unitsingle syntactic unit

e.g., e.g., Stack stk1, stk2; create(stk1); create(stk2); …Stack stk1, stk2; create(stk1); create(stk2); …

push(stk1, color1); color2 = pop(stk2);push(stk1, color1); color2 = pop(stk2);

The The representation of objects of the type is hiddenrepresentation of objects of the type is hidden from the program units that use these objects, so the from the program units that use these objects, so the only operations possible are those providedonly operations possible are those provided in the in the type's definitiontype's definition

Clients of a Data TypeClients of a Data Type: Program units that use : Program units that use a specific abstract data typea specific abstract data type

Spring 2005 14


An Example of Abstract Data TypesAn Example of Abstract Data Types

class class StackStack extends Vector { extends Vector {public public Stack()Stack() { // create{ // create

super();super(); }}

public public Object push(Object item)Object push(Object item) { {addElement(item);addElement(item);

}}public public Object pop()Object pop() {{

int top = size() – 1;int top = size() – 1;if (top < 0) return null;if (top < 0) return null;elseelse return elementAt(top);return elementAt(top);

}}……

} // } // Implementation of the stackImplementation of the stack //// data type in Java using a data type in Java using a VectorVector Change to use a Change to use a

Linked ListLinked List

The client doesn’t The client doesn’t need to be changedneed to be changed

A ClientA Client

StackStack stk1 = stk1 =new new Stack()Stack();;

stk1.stk1.pushpush(“1st ele”);(“1st ele”);stk1.stk1.pushpush( “2nd ele”);( “2nd ele”);……String ele =String ele = (String)stk1.(String)stk1.poppop();();

Spring 2005 15


Design Issues for Abstract Data TypesDesign Issues for Abstract Data Types

EncapsulationEncapsulation: A syntactic unit in which to : A syntactic unit in which to encapsulate the encapsulate the type definitiontype definition

Information HidingInformation Hiding: A method of : A method of making type making type names and subprogram headers visible to names and subprogram headers visible to clientsclients, while hiding actual definitions, while hiding actual definitions

Some Some primitive operationsprimitive operations must be built into the must be built into the language processor (usually just language processor (usually just assignmentassignment and and comparisonscomparisons for equality and inequality) for equality and inequality) Some operations are commonly needed, but must be Some operations are commonly needed, but must be

defined by the type designerdefined by the type designer

e.g., e.g., iterators, constructors, destructorsiterators, constructors, destructors* AW Lecture Notes

Spring 2005 16


Abstract Data Types in AdaAbstract Data Types in Ada

EncapsulationEncapsulation construct: ‘construct: ‘packagepackage’’

Information hidingInformation hiding via via the ‘the ‘privateprivate’ part’ part

Specification PackageSpecification Package: : an an interface of an interface of an encapsulationencapsulation (visible (visible to clients)to clients)

Body PackageBody Package: : implementation implementation (hidden from clients)(hidden from clients)

A A client client of the package of the package Linked_List_TypeLinked_List_Type

packagepackage Linked_List_Type is Linked_List_Type istype type Node_TypeNode_Type is private; is private;……privateprivate type Node_Type;type Node_Type; type Ptr is access Node_Type;type Ptr is access Node_Type; type Node_Type istype Node_Type is

recordrecord Info : Integer;Info : Integer; Link : Ptr;Link : Ptr;end record;end record;

end Linked_List_Type;end Linked_List_Type;……useuse Linked_List_Type; Linked_List_Type;procedureprocedure Use_Linked_Lists Use_Linked_Lists isis

Node : Node : Node_TypeNode_Type;;

Spring 2005 17


Abstract Data Types in C++Abstract Data Types in C++ Data MembersData Members ConstructorConstructor

InitializesInitializes the data members the data members Implicitly calledImplicitly called when an instance is when an instance is

created (Can be explicitly called)created (Can be explicitly called) Name is the same as the class nameName is the same as the class name

DestructorDestructor CleanupCleanup after an instance is after an instance is

destroyed (e.g., free heap storage)destroyed (e.g., free heap storage) Implicitly calledImplicitly called when the object’s when the object’s

lifetime ends (Can be explicitly called)lifetime ends (Can be explicitly called) Name is the class name, preceded by Name is the class name, preceded by

a tilde (~)a tilde (~)

Member FunctionsMember Functions

class stack {class stack {private: int private: int *ptr, max, top*ptr, max, top;;public: public: stack()stack() { { ptr = new int [100];ptr = new int [100]; max = 99;max = 99; top = -1;top = -1;}}~stack()~stack() { delete [] ptr; }; { delete [] ptr; };void push(int num)void push(int num) { { if (top < max)if (top < max)

ptr[++top] = num;ptr[++top] = num;}}……

}}

Spring 2005 18


Abstract Data Types in C++Abstract Data Types in C++

EncapsulationEncapsulation by by classesclasses Each instance of a class has its Each instance of a class has its

own copy of own copy of data membersdata members Class instances share a single copy Class instances share a single copy

of the of the member functionsmember functions Instances can be static, stack Instances can be static, stack

dynamic, or heap dynamicdynamic, or heap dynamic

Information HidingInformation Hiding PrivatePrivate clause clause for hidden entities for hidden entities PublicPublic clause clause for interface entities for interface entities

Client partClient partCreates an instanceCreates an instance

Access a member functionAccess a member function

classclass stackstack { {privateprivate: int *ptr, max, top;: int *ptr, max, top;publicpublic: : stack()stack() { { ptr = new int [100];ptr = new int [100]; max = 99;max = 99; top = -1;top = -1;}}~stack()~stack() { delete [] ptr; }; { delete [] ptr; };void push(int num)void push(int num) { { if (top < max)if (top < max)


}}void main() {void main() {

stack stk;stack stk;stk.push(42); …stk.push(42); …

Spring 2005 19


Abstract Data Types in C#Abstract Data Types in C#

Accessor methodsAccessor methods ((gettersgetters and and setterssetters): ): allow indirect access allow indirect access to hidden data to hidden data membersmembers

C# provides C# provides propertiesproperties as a way as a way of implementing of implementing getters and setters getters and setters without requiring without requiring explicit method callsexplicit method calls

public class public class WeatherWeather { {public int public int DegreeDaysDegreeDays { { getget { {

return degreeDays;return degreeDays; } } setset { {

degreeDays = value;degreeDays = value; }}}}private int degreeDays;private int degreeDays;......

}}......Weather w = new Weather();Weather w = new Weather();int todaysDegree, oldDegree; …int todaysDegree, oldDegree; …w.DegreeDays = todaysDegree;w.DegreeDays = todaysDegree;oldDegree = w.DegreeDays;oldDegree = w.DegreeDays;

Spring 2005 20


Parameterized Abstract Data TypesParameterized Abstract Data Types

Making the stack class Making the stack class usable for usable for any data any data typetype and and arbitrary arbitrary maximum sizemaximum size

Making the class a Making the class a templated classtemplated class

Using Using parameterized parameterized constructorconstructor functions functions

templatetemplate <class <class TypeType>>class stack {class stack {

private: int *ptr, max, top;private: int *ptr, max, top;public: stack(int public: stack(int sizesize) {) { ptr = new ptr = new TypeType [ [sizesize];]; max = max = sizesize - 1; - 1; top = -1;top = -1;}}~stack() { delete [] ptr; };~stack() { delete [] ptr; };void push(int num) {void push(int num) { if (top < max)if (top < max)


}}C++

Spring 2005 21


Encapsulation & Information HidingEncapsulation & Information Hiding In Java or C++, both In Java or C++, both data membersdata members and and member functionsmember functions

are defined in a classare defined in a class An An interfaceinterface hides the implementation detailshides the implementation details of data of data

structures and functions of an objectstructures and functions of an object Information hidingInformation hiding ensures the ensures the data integritydata integrity by preventing by preventing

programmers from accessing data incorrectlyprogrammers from accessing data incorrectly

FriendFriend

<<constructor>><<constructor>> Friend(name: String) Friend(name: String)+ getName() : String+ getName() : String+ setName(name: String)+ setName(name: String)+ getEmail() : String+ getEmail() : String+ setEmail(email: String)+ setEmail(email: String)……

An interface to access the objectAn interface to access the object

public class public class FriendFriend { {private String name, email, phone;private String name, email, phone;public public FriendFriend ( String name ) { ( String name ) {

this.name = name;this.name = name;}}public String getName() {public String getName() {

return name;return name;}}public viod setName(String name) {public viod setName(String name) {

this.name = name;this.name = name;}}……

}}

Spring 2005 22


Encapsulation ConstructsEncapsulation Constructs

Motivation – Large programs with thousands of Motivation – Large programs with thousands of lines have two special needs:lines have two special needs:1. Some 1. Some means of organizationmeans of organization to keep them to keep them

intellectually manageableintellectually manageable

2. Some 2. Some means of partial compilationmeans of partial compilation (compilation (compilation units that are smaller than the whole program)units that are smaller than the whole program)

Solution – Solution – EncapsulationEncapsulation: a : a grouping of grouping of subprogramssubprograms that are logically related into a that are logically related into a unit that can be separately compiled unit that can be separately compiled ((compilation unitscompilation units))

e.g., Java e.g., Java packagespackages, C library & , C library & header filesheader files* AW Lecture Notes

Spring 2005 23


Java PackagesJava Packages

Spring 2005 24


Naming Encapsulations (1)Naming Encapsulations (1)

Large programs define Large programs define many global namesmany global names; ; need need a way to divide into logical groupingsa way to divide into logical groupings

A A naming encapsulationnaming encapsulation is used to create a is used to create a new scope for namesnew scope for names

C++, C# C++, C# NamespacesNamespaces – One can place each – One can place each library in its own namespace and qualify names library in its own namespace and qualify names used outside with the namespaceused outside with the namespace

namespace Stack1 {namespace Stack1 { namespace Stack2 namespace Stack2 {{

int top; …int top; … int top; … int top; …}} }}Stack1::top = Stack2::top;Stack1::top = Stack2::top; * AW Lecture Notes

Spring 2005 25


Naming Encapsulations (2)Naming Encapsulations (2)

Java Java PackagesPackages Packages can contain Packages can contain more than one class more than one class

definitiondefinition; classes in a package are ; classes in a package are partial friendspartial friends Clients use fully qualified names (e.g., Clients use fully qualified names (e.g., java.io.Filejava.io.File) or ) or

use the ‘use the ‘importimport’ declaration (e.g., ’ declaration (e.g., import java.io.*;import java.io.*;)) Ada Ada PackagesPackages

Packages are defined in hierarchies which Packages are defined in hierarchies which correspond to file hierarchiescorrespond to file hierarchies

VisibilityVisibility from a program unit is gained with the ‘ from a program unit is gained with the ‘withwith’ ’ clause (e.g., clause (e.g., with Ada.Text_IO;with Ada.Text_IO;))

To To access names without qualificationaccess names without qualification, the ‘, the ‘useuse’ ’ clause can be used (e.g., clause can be used (e.g., use Ada.Text_IOuse Ada.Text_IO))

* AW Lecture Notes

Documents

ICE1341 Programming Languages Spring 2005 Lecture #18 Lecture #18 In-Young Ko iko.AT. icu.ac.kr iko.AT. icu.ac.kr Information and Communications University