OOP Chapter 8 : Inheritance

Object-Oriented Programming Language
Chapter 8 : Inheritance

Atit Patumvan
Faculty of Management and Information Sciences
Naresuan University

2

It All Begins at the Root

@interface Fraction: NSObject
:
@end

NSObject
root class or superclass

Fraction
subclass

Atit Patumvan, Faculty of Management and Information Sciences, Naresuan University Object-Oriented Programming Language

3

Subclasses and superclasses

@interface ClassA: NSObject
{
! int x;
NSObject }

-(void) initVar;
@end
subclass superclass @implementation ClassA
-(void) initVar
{
! x = 100;
ClassA }
@end

@interface ClassB: ClassA
subclass superclass -(void) printVar;
@end

@implementation ClassB
-(void) printVar
ClassB {
! NSLog(@"x= %i", x);
}
@end

4

Subclasses and superclasses

@interface ClassA: NSObject
{
! int x;
Class Instance Variables Methods
}

-(void) initVar; NSObject
@end

@implementation ClassA
-(void) initVar
{
! x = 100;
}
@end ClassA x initVar

@interface ClassB: ClassA
-(void) printVar;
@end

-(void) printVar
{ ClassB x intVar printVar
! NSLog(@"x= %i", x);
}
@end

5

Simple Inheritance

Program 8.1 main.m
:
28: int main(int argc, char *argv[]) {
29:! NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
30:!
31:! ClassB * b = [[ClassB alloc] init];
32:!
33:! [b initVar];
34:! [b printVar]; // x = 100
35:!
36:! [b release];
@interface ClassA: NSObject @interface ClassB: ClassA
37:!
{ -(void) printVar;
38:! [pool drain];
! int x; @end
39:! return 0;!
}
40:! }
41: }
-(void) initVar; -(void) printVar
:
@end {
! NSLog(@"x= %i", x);
@implementation ClassA }
-(void) initVar @end
{
! x = 100;
}
@end


6

Extension Through Inheritance: Adding New Methods

Program 8.2 Rectangle.h
01: #import <Foundation/Foundation.h>
02:
03: @interface Rectangle: NSObject
04: {
05:! int width;
06:! int height;
07: }
08:
09: @property int width, height;
10:
11: -(void) setWidth: (int) w andHeight: (int) h; Program 8.2 Rectangle.m
12: -(int) area;
13: -(int) perimeter; 01: #import "Rectangle.h"
14: 02:
15: @end 03: @implementation Rectangle
04:
05: @synthesize width, height;
06:
07: -(void) setWidth: (int) w andHeight: (int) h
08: {
09:! width = w;
10:! height = h;
11: }
:
21: @end

7

Extension Through Inheritance: Adding New Methods

02:#import "Rectangle.h"
03:
04: int main(int argc, char *argv[]) {
05:! NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
06:! Rectangle * myRect = [[Rectangle alloc] init ];
07:!
08:! [myRect setWidth: 5 andHeight: 8];
09:!
10:! NSLog(@"Rectangle: w = %i, h = %i", myRect.width, myRect.height);
11:! NSLog(@"Area = %i, Perimeter = %i", [myRect area], [myRect perimeter]);
12:!
13:! [myRect release];
14:! [pool drain];
15:! return 0;
16: }


8

Extension Through Inheritance: Subclassing

Program 8.3 Square.h Program 8.3 main.m
01: #import <Foundation/Foundation.h> 01: #import <Foundation/Foundation.h>
02: #import "Rectangle.h" 02: #import "Square.h"
03: 03:
04: @interface Square : Rectangle 04: int main (int argc, char * argv[])
05: 05: {
06: -(void) setSide: (int) s; 06: NSAutoreleasePool * pool =
07: -(int) side; [[NSAutoreleasePool alloc] init];
08: @end 07:
08: Square * mySquare = [[Square alloc] init];
Program 8.3 Square.m 09:
10: [mySquare setSide: 5];
01: #import "Square.h" 11:
02: 12: NSLog(@"Square s = %i", [mySquare side]);
03: @implementation Square: Rectangle 13: NSLog(@"Area = %i, Perimeter = %i",
04: [mySquare area], [mySquare perimeter]);
05: -(void) setSide: (int) s 14:
06: { 15: [pool drain];
07:! [self setWidth: s andHeight: s]; 16: return 0;
08: } 17:
09: 18: }
10: -(int) side
11: {
12:! return width;!
13: }
14: @end

9

A Point Class and Memory Allocation

(x,y)

y myRect
(x1,y1)

(0,0) x
Program 8.4 XYPoint.h Program 8.4 Rectangle.h
01: #import <Foundation/Foundation.h> :
02: 05: @interface Rectangle: NSObject
03: @interface XYPoint: NSObject 06: {
04: { 07:! int width;
05: int x; 08:! int height;
06: int y; 09: XYPoint * origin;
07: } 10: }
08: @property int x, y; 11:
09: :
10: -(void) setX: (int) xVal andY: (int) yVal; 13: -(XYPoint *) origin;
11: @end :

10

The @class directive

02:
03: @class XYPoint;
04:
@class directive
05: @interface Rectangle: NSObject
06: {
07:! int width;
08:! int height;
09: XYPoint * origin;
10: }
11:
12: @property int width, height;
13: -(XYPoint *) origin;
14: -(void) setOrigin: (XYPoint *) pt;
15: -(void) setWidth: (int) w andHeight: (int) h;
16: -(int) area;
17: -(int) perimeter;
18:
19: @end


11

Handling Object in Method

Program 8.4 Rectangle.h Program 8.4 Rectangle.m
01: #import <Foundation/Foundation.h> 01: #import "Rectangle.h"
02: 02:
03: @class XYPoint; 03: @implementation Rectangle
04: 04:
05: @interface Rectangle: NSObject 05: @synthesize width, height;
06: { 06:
07:! int width; 07: -(XYPoint *) origin
08:! int height; 08: {
09: XYPoint * origin; 09: return origin;
10: } 10: }
11: 11: -(void) setOrigin: (XYPoint *) pt
12: @property int width, height; 12: {
13: -(XYPoint *) origin; 13: origin = pt;
14: -(void) setOrigin: (XYPoint *) pt; 14: }
15: -(void) setWidth: (int) w andHeight: (int) h; :
16: -(int) area;
17: -(int) perimeter;
18:
19: @end


12

Handling Object in Method

Program 8.4 main.m
02: #import "Rectangle.h"
03: #import "XYPoint.h"
:
09: Rectangle * myRect = [[Rectangle alloc] init];
10: XYPoint * myPoint = [[XYPoint alloc] init];
11:
12: [myPoint setX: 100 andY: 200];
13:
14: [myRect setWidth: 5 andHeight: 8];
15: myRect.origin = myPoint;
16:
17: NSLog(@"Rectangle w = %i, h = %i", myRect.width, myRect.height);
18:
19: NSLog(@"Origin at (%i, %i)", myRect.origin.x, myRect.origin.y);
20:
21: NSLog(@"Area = %i, Perimeter = %i", [myRect area], [myRect perimeter]);
22:
23: [myRect release];
24: [myPoint release];
:


13

Can you explain the output from Program 7.5?

Program 8.5 main.m
:
09: Rectangle * myRect = [[Rectangle alloc] init];
10: XYPoint * myPoint = [[XYPoint alloc] init];
11:
13:
14: [myRect setWidth: 5 andHeight: 8];
15: myRect.origin = myPoint;
16:
18:
20:
22:
23: [myRect release];
24: [myPoint release]; myPoint
25:
26: [pool drain];
27: return 0; myRect width = 5 x = 100
: height = 8 y = 200
origin XYPoint@yyyy
Rectangle@xxxx


14

Fixing Reference Problem

Program 8.5B Rectangle.m Program 8.5B main.m
: :
12: -(void) setOrigin: (XYPoint *) pt 23: [[myRect origin] release];
13: { 24: [myRect release];
14: if (! origin) 25: [myPoint release];
15: origin = [[XYPoint alloc] init]; :
16:
17: origin.x = pt.x;
18: origin.y = pt.y;
19: }
:

myPoint

myRect width = 5 x = 100
height = 8 y = 200
origin XYPoint@yyyy pt

Rectangle@xxxx
x = 100
y = 200 copy

XYPoint@zzzz


15

Overriding Methods

Program 8.6 main.m
: :
07: @interface ClassA : NSObject { 22: @interface ClassB : ClassA
08: int x; 23: -(void) initVar;
09: } 24: -(void) printVar;
10: 25: @end
11: -(void) initVar; 26:
12: @end 27: @implementation ClassB
13: 28: -(void) initVar
14: @implementation ClassA 29: {
15: -(void) initVar 30: x = 200;
16: { 31: }
17: x = 100; 32: -(void) printVar
18: } 33: {
19: 34: NSLog(@"x = %i", x);
20: @end 35: }
: 36: @end
:
:
41: ClassB * b = [[ClassB alloc] init];
42:
43: [b initVar]; // uses overrinding method in B
44:
45: [b printVar]; // reveal value of x;
46: [b release];
:

16

Overriding Methods: Which method is Selected?

Program 8.7 main.m (old) Program 8.7 main.m (new)
:
07: @interface ClassA : NSObject { :
08: int x; 12: -(void) printVar;
09: } 13: @end
10: 14:
11: -(void) initVar; 15: @implementation ClassA
12: @end 16: -(void) initVar
13: 17: {
14: @implementation ClassA 18: x = 100;
15: -(void) initVar 19: }
16: { 20: -(void) printVar
17: x = 100; 21:
18: } 22: NSLog(@"x = %i", x);
19: 23: }
20: @end :
:
:
42: ClassA * a = [[ClassA alloc] init];
43: ClassB * b = [[ClassB alloc] init];
44: [a initVar]; // uses ClassA method
45: [a printVar]; // reveal value of x
46:
47: [b initVar]; // uses overrinding ClassB method
48: [b printVar]; // reveal value of x;
:

17

Overriding the dealloc Method and the Keyword super

Program 8.5B Rectangle.m Program 8.5B main.m
: :
12: -(void) setOrigin: (XYPoint *) pt 23: [[myRect origin] release];
14: if (! origin) 25: [myPoint release];
15: origin = [[XYPoint alloc] init]; :
16:
17: origin.x = pt.x;
18: origin.y = pt.y;
19: }
:
Text
Program 8.7B Rectangle.m
Program 8.7B main.m
:
33: -(void) dealloc :
35: if(origin) 24: [myPoint release];
36: [origin release]; :
37: [super dealloc];
38: }
:
overriding dealloc method
keyword super

18

Extension Through Inheritance: Adding New Instance Variables

Program 8.8 main.m Program 8.8 main.m
: :
07: @interface ClassA : NSObject { 22: @interface ClassB : ClassA
08: int x; 23: {
09:} 24: int y;
10: 25: }
11:-(void) initVar; 26:
12: 27: -(void) initVar;
13:@end 28: -(void) printVar;
14:
15:@implementation ClassA
Text 29:
30:
@end

16:-(void) initVar 31: @implementation ClassB
17:{ 32: -(void) initVar
18: x = 100; 33: {
19:} 34: x = 200;
20:@end 35: y = 300;
: 36: }
37: -(void) printVar
: 38: {
48: ClassB * b = [[ClassB alloc] init]; 39: NSLog (@"x = %i", x);
49: 40: NSLog (@"y = %i", y);
50: [b initVar]; 41: }
51: [b printVar]; 42: @end
: :


OOP Chapter 8 : Inheritance

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