Program 8.8

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Program 8.8

Code: (Objective-C)

// Extension of instance variables

#import <Foundation/Foundation.h>

// ClassA declaration and definition

@interface ClassA : NSObject
{
	int x;
}

-(void) initVar;
@end

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

// ClassB declaration and definition

@interface ClassB : ClassA
{
	int y;
}
-(void) initVar;
-(void) printVar;
@end

@implementation ClassB
-(void) initVar
{
	x = 200;
	y = 300;
}

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


int main (int argc, char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    ClassB *b = [[ClassB alloc] init];
	
	[b initVar];   // uses overriding method in ClassB
	[b printVar];  // reveal values of x and y;
	
	[b release];
    [pool drain];
    return 0;
}