OOP Chapter 3: Classes, Objects and Methods

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

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

3

What Is an Object, Anyway?

Class Instance/Object
create from
Car myCar:Car

create from
yourCar:Car


4

Instances and Methods

[ ClassOrInstance method ];

yourCar = [Car new];

message
yourCar:Car
receiver
Sender

[yourCar drive];
[yourCar getGas: 30];
currentMileage = [yourCar odometer];

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: }
:


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
:


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
:


8

The program Section

Program 3.2
:
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: }

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
:


10

Accessing Instance Variables and Data Encapsulation

Program 3.4
:
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: }


OOP Chapter 3: Classes, Objects and Methods

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