object-c的继承

ゝ一纸荒年。 2023-10-18 21:35 4阅读 0赞

作为面向对象的编程语言，object-c当然也支持继承，而且和java一样，支持的是单一继承，即只有一个超类。  
当然，也支持覆盖（或重写）父类的同名方法。例子如下：  
  
  
 **1. 代码**：  
 //1. MyRectangle.h  
\#import <Foundation/NSObject.h>  
  
  
@interface MyRectangle: NSObject \{  
int width;  
int height;  
\}  
  
  
\-(MyRectangle\*) initWithWidth: (int) w height: (int) h;  
\-(void) setWidth: (int) w;  
\-(void) setHeight: (int) h;  
\-(void) setWidth: (int) w height: (int) h;  
\-(int) width;  
\-(int) height;  
\-(void) print;  
@end  
  
//2. MyRectangle.m  
  
\#import "MyRectangle.h"  
\#import <stdio.h>  
  
@implementation MyRectangle  
\-(MyRectangle\*) initWithWidth: (int) w height: (int) h \{  
self = \[super init\];  
  
  
if ( self ) \{  
\[self setWidth: w height: h\];  
\}  
  
  
return self;  
\}  
  
  
\-(void) setWidth: (int) w \{  
width = w;  
\}  
  
  
\-(void) setHeight: (int) h \{  
height = h;  
\}  
  
  
\-(void) setWidth: (int) w height: (int) h \{  
width = w;  
height = h;  
\}  
  
  
\-(int) width \{  
return width;  
\}  
  
  
\-(int) height \{  
return height;  
\}  
  
  
\-(void) print \{  
printf( "width = %i, height = %i", width, height );  
\}  
@end  
  
  
//3. Square.h  
\#import "MyRectangle.h"  
  
  
@interface Square: MyRectangle  
\-(Square\*) initWithSize: (int) s;  
\-(void) setSize: (int) s;  
\-(int) size;  
@end  
  
  
  
  
//4. Square.m  
\#import "Square.h"  
  
  
@implementation Square  
\-(Square\*) initWithSize: (int) s \{  
self = \[super init\];  
  
  
if ( self ) \{  
\[self setSize: s\];  
\}  
  
  
return self;  
\}  
  
  
\-(void) setSize: (int) s \{  
width = s;  
height = s;  
\}  
  
  
\-(int) size \{  
return width;  
\}  
  
  
\-(void) setWidth: (int) w \{  
\[self setSize: w\];  
\}  
  
  
\-(void) setHeight: (int) h \{  
\[self setSize: h\];  
\}  
@end  
  
  
  
  
//5. main.m  
\#import "Square.h"  
\#import "MyRectangle.h"  
\#import <stdio.h>  
  
  
int main( int argc, const char \*argv\[\] ) \{  
MyRectangle \*rec = \[\[MyRectangle alloc\] initWithWidth: 10 height: 20\];  
Square \*sq = \[\[Square alloc\] initWithSize: 15\];  
  
  
// print em  
printf( "MyRectangle: " );  
\[rec print\];  
printf( "\\n" );  
  
  
printf( "Square: " );  
\[sq print\];  
printf( "\\n" );  
  
  
// update square  
\[sq setWidth: 20\];  
printf( "Square after change: " );  
\[sq print\];  
printf( "\\n" );  
  
  
//调用继承自父类的width和height  
printf( "Square after width: %i\\n", \[sq width\] );  
printf( "Square after height: %i", \[sq height\] );  
// free memory  
\[rec release\];  
\[sq release\];  
  
return 0;  
\}  
  
2. 编译运行 ：  
gcc -fconstant-string-class=NSConstantString -c main.m -I /GNUstep/System/Library/Headers  
gcc -c MyRectangle.m -I /GNUstep/System/Library/Headers  
gcc -c Square.m -I /GNUstep/System/Library/Headers  
gcc main.o Square.o MyRectangle.o -o main -L /GNUstep/System/Library/Libraries/ -lobjc -lgnustep-base  
  
$ ./main.exe  
MyRectangle: width = 10, height = 20  
Square: width = 15, height = 15  
Square after change: width = 20, height = 20

Square after width: 20Square after height: 20

**3. 说明：**  
（1） Square继承自MyRectangle,重写了setWidth和setHeight方法；  
（2） Square可以调用继承自父类MyRectangle的width和height方法。