繼承 - paraquat的部落格

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繼承

2011/02/20 21:08:20瀏覽378｜回應0｜推薦0

這是Programming in Objective-C 2.0第八章的內容，用來介紹物件導向的繼承（inheritance）。

長方型類別（Rectangle class）裡面定義了二個整數instance variables，且定了setter and getter methods來對這二個instance variables進行存取的工作，另外定義了算週長，面積等methods。

正方型是長方型的一種，它的定義和長方型一樣，但是它的長、寛相等。如正方型類（Square class)繼承長方型類，則長方型類所有的methods，正方型的物件都可以使用。下面是例子：

Rectangle.h:

#import ＜Foundation/Foundation.h＞

@interface Rectangle : NSObject {

int width;

int height;

}

@property int width, height;

-(void) setWidth: (int) w andHeight: (int) h;

-(int) area;

-(int) perimeter;

-(Rectangle *) initWithWidth: (int) w andHeight: (int) h;

@end

Rectangle.m:

#import "Rectangle.h"

@implementation Rectangle

@synthesize width, height;

-(void) setWidth: (int) w andHeight: (int) h{

width=w;

height=h;

}

-(int) area{

return width * height;

}

-(int) perimeter{

return 2*width+2*height;

}

-(Rectangle *) initWithWidth: (int) w andHeight: (int) h{

self = [super init];

if (self)

[self setWidth:w andHeight:h];

return self;

}

@end

Square.h:

#import "Rectangle.h"

@interface Square : Rectangle

-(void) setSide:(int)s;

-(int) side;

-(Square *)initWithSide: (int) s;

@end

Square.m:

#import "Square.h"

@implementation Square

-(void) setSide: (int) s{

[self setWidth:s andHeight:s];

}

-(int) side{

return width;

}

-(Square *)initWithSide: (int) s{

self=[super init];

if (self)

[self setSide:s];

return self;

}

@end

主程式：

#import ＜Foundation/Foundation.h＞

#import "Square.h"

int main (int argc, const char * argv[]) {

NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

Rectangle *myRect = [[Rectangle alloc] initWithWidth:5 andHeight:8];

Square *mySquare = [[Square alloc] initWithSide:5];

NSLog(@"長方型w=%i,h=%i", myRect.width, myRect.height);

NSLog(@"長方型面積Area = %i, 週長Perimeter = %i",[myRect area],[myRect perimeter]);

NSLog(@"正方型邊長s=%i", [mySquare side]);

NSLog(@"正方型面積Area = %i, 週長Perimeter = %i",[mySquare area],[mySquare perimeter]);

[myRect release];

[pool drain];

return 0;

}

編譯執行結果：

長方型w=5,h=8

長方型面積Area = 40, 週長Perimeter = 26

正方型邊長s=5

正方型面積Area = 25, 週長Perimeter = 20

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