An objective C example demonstrating the concept of inheritance.

Animal.h

//
//  Animal.h
//  InheritanceDemo
//
//  Created by Rajiv on 14/07/2011.
//  Copyright 2011 WebileApps. All rights reserved.
//

#import <Foundation/Foundation.h>


@interface Animal : NSObject {

}

-(void) shout;

-(void) noOfEyes;

-(void) doSomeTask;

@end

@interface Dog : Animal {

}

//A parent method which is over ridden in child.
-(void) shout;

//A new method belonging to this class.
-(void) swim;

//Another function overridden in child class
-(void) doSomeTask;

@end

Animal.m

//
//  Animal.m
//  InheritanceDemo
//
//  Created by Rajiv on 14/07/2011.
//  Copyright 2011 Webile Apps. All rights reserved.
//

#import "Animal.h"


@implementation Animal

-(void) shout {
	NSLog(@"Animal: Not sure how does I shout");
}

-(void) noOfEyes {
	NSLog(@"Animal: I have 2 eyes");
}

-(void) doSomeTask {
	NSLog(@"Animal: I am doing some task");
}

@end

@implementation Dog

-(void) shout {
	NSLog(@"Dog: Wow wow..");
}

-(void) swim {
	NSLog(@"Dog: I am swimming");
}

-(void) doSomeTask {
	[super doSomeTask];
	NSLog(@"Dog: I am doing some task");
}
@end

Output.txt

2011-07-14 00:35:05.572 InheritanceDemo[84631:207] Animal: Not sure how does I shout
2011-07-14 00:35:05.573 InheritanceDemo[84631:207] Animal: I am doing some task
2011-07-14 00:35:05.574 InheritanceDemo[84631:207] Animal: I have 2 eyes
2011-07-14 00:35:05.575 InheritanceDemo[84631:207] Dog: Wow wow..
2011-07-14 00:35:05.575 InheritanceDemo[84631:207] Dog: I am swimming
2011-07-14 00:35:05.576 InheritanceDemo[84631:207] Animal: I have 2 eyes
2011-07-14 00:35:05.576 InheritanceDemo[84631:207] Animal: I am doing some task
2011-07-14 00:35:05.577 InheritanceDemo[84631:207] Dog: I am doing some task

SomeOtherFile.m

-(void) someFunction {
	Animal *animal = [[Animal alloc] init];
	[animal shout];
	[animal doSomeTask];
	
	//	[animal swim]; //Generates comile time errors
	
	[animal noOfEyes];

	Dog *dog = [[Dog alloc] init];
	[dog shout];
	[dog swim];
	[dog noOfEyes];
	[dog doSomeTask];
}