This document discusses object-oriented programming concepts like classes, objects, and methods. It provides an example class for representing fractions that defines instance variables to store the numerator and denominator. It demonstrates creating fraction objects, setting properties on objects by calling methods, and accessing instance variables. The class defines an interface with method signatures and an implementation that includes method definitions to print fractions, set property values, and return property values.

1. Object-Oriented Programming Language
Chapter 3 : Classes, Objects, and Methods
Atit Patumvan
Faculty of Management and Information Sciences
Naresuna University
Monday, November 21, 2011

2. 2
Contents
• What Is an Object, Anyway?
• Instances and Methods
• An Objective-C Class for Working with Fractions
• The @interface Section
• The @implementation Section
• The program Section
• Accessing Instance Variable and Data Encapsulation
Atit Patumvan, Faculty of Management and Information Sciences, Naresuan University Object-Oriented Programming Language
Monday, November 21, 2011

3. 3
What Is an Object, Anyway?
Class Instance/Object
create from
Car myCar:Car
create from
yourCar:Car
Atit Patumvan, Faculty of Management and Information Sciences, Naresuan University Object-Oriented Programming Language
Monday, November 21, 2011

4. 4
Instances and Methods
[ ClassOrInstance method ];
yourCar = [Car new];
message
yourCar:Car
receiver
Sender
[yourCar drive];
[yourCar getGas: 30];
currentMileage = [yourCar odometer];
Atit Patumvan, Faculty of Management and Information Sciences, Naresuan University Object-Oriented Programming Language
Monday, November 21, 2011

5. 5
An Objective-C Class for Working with Fractions
Program 3.1
01: #import <Foundation/Foundation.h>
02:
03: int main (int argc, const char * argv[]) {
04: NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
05:
06:
int numerator = 1;
07:
int denominator = 3;
08:
09: NSLog(@"The fraction is %i/%i", numerator, denominator);
10: [pool drain];
11: return 0;
12: }
:
Atit Patumvan, Faculty of Management and Information Sciences, Naresuan University Object-Oriented Programming Language
Monday, November 21, 2011

6. 6
The @interface Section
Program 3.2
:
03: //---- @interface section ---- Fraction
04:
05: @interface Fraction: NSObject numerator:int
06: {
07:
int numerator;
denominator:int
08:
int denominator;
09: } print:void
10: setNumerator(int):void
11: -(void) print; setDenominator(int):void
12: -(void) setNumerator: (int) n;
13: -(void) setDenominator: (int) d;
14:
15: @end
:
Atit Patumvan, Faculty of Management and Information Sciences, Naresuan University Object-Oriented Programming Language
Monday, November 21, 2011

7. 7
The @implementation Section
Program 3.2
:
18: Fraction
19: @implementation Fraction
20:
21: -(void) print
numerator:int
22: { denominator:int
23:
NSLog (@"%i/%i", numerator, denominator);
24: } print:void
25: setNumerator(int):void
26: -(void) setNumerator: (int) n;
27: {
setDenominator(int):void
28:
numerator = n;
29: }
30:
31: -(void) setDenominator: (int) d;
32: {
33:
denominator = d;
34: }
35:
36: @end
:
Atit Patumvan, Faculty of Management and Information Sciences, Naresuan University Object-Oriented Programming Language
Monday, November 21, 2011

8. 8
The program Section
Program 3.2
:
40: int main (int argc, const char * argv[]) {
41: NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
42:
43: // insert code here...
44:
Fraction * myFraction; Fraction
45:
46:
myFraction = [Fraction alloc]; numerator:int
47:
myFraction = [myFraction init];
48:
denominator:int
49:
Set fraction to 1/3;
//
50:
print:void
51:
[myFraction setNumerator: 1]; setNumerator(int):void
52:
[myFraction setDenominator: 3]; setDenominator(int):void
53:
54:
Display the fraction using the print method
//
55:
56:
NSLog(@"The value of myFraction is:");
57:
[myFraction print]; myFraction:Fraction
58:
59:
[myFraction release];
60:
61:
[pool drain];
62: return 0;
63: }
Atit Patumvan, Faculty of Management and Information Sciences, Naresuan University Object-Oriented Programming Language
Monday, November 21, 2011

9. 9
Accessing Instance Variables and Data Encapsulation
Program 3.4
01: @interface Fraction: NSObject Fraction
:
10: -(int) numerator;
11: -(int) denominator; numerator:int
12: denominator:int
13: @end
: print():void
17: @implementation Fraction setNumerator(int):void
18:
: setDenominator(int):void
34: -(int) numerator numerator():int
35: { denominator():int
36:
return numerator;
37: }
38:
39: -(int) denominator
40: {
41:
return denominator;
42: }
43:
44: @end
:
Atit Patumvan, Faculty of Management and Information Sciences, Naresuan University Object-Oriented Programming Language
Monday, November 21, 2011

10. 10
Accessing Instance Variables and Data Encapsulation
Program 3.4
:
52: int main (int argc, const char * argv[]) {
53: NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
54:
55: // insert code here...
56:
Fraction * myFraction = [[Fraction alloc] init]; Fraction
57:
58:
Set fraction to 1/3;
//
59:
numerator:int
60:
[myFraction setNumerator: 1]; denominator:int
61:
[myFraction setDenominator: 3];
62:
print():void
63:
Display the fraction using our two new methods
// setNumerator(int):void
64: setDenominator(int):void
65:
NSLog(@"The value of myFraction is:%i/%i",
numerator():int
66:
[myFraction numerator],
67:
[myFraction denominator]); denominator():int
68:
69:
[myFraction release];
70:
71:
[pool drain];
72: return 0;
73: }
Atit Patumvan, Faculty of Management and Information Sciences, Naresuan University Object-Oriented Programming Language
Monday, November 21, 2011