Objective-C 繼承

在面向對象的編程中最重要的概念之一是繼承。繼承允許我們定義一個類在另一個類，這使得它更容易創(chuàng)建和維護應用程序方面。這也提供了一個機會，重用代碼的功能和快速的執(zhí)行時間。

當創(chuàng)建一個類，而不是寫入新的數(shù)據(jù)成員和成員函數(shù)，程序員可以指定新的類繼承現(xiàn)有類的成員。這種現(xiàn)有的類稱為基類，新類稱為派生類。

繼承的想法實現(xiàn)是有關系的。例如，哺乳動物是一個動物，狗是哺乳動物，因此狗是動物等。

基類和派生類：

Objective-C中允許多重繼承，也就是說，它只能有一個基類，但允許多層次的繼承。Objective-C中的所有類的超類為NSObject。

@interface derived-class: base-class

考慮一個基類 Shape 和它的派生類Rectangle 如下：

#import <Foundation/Foundation.h>
 
@interface Person : NSObject

{
    NSString *personName;
    NSInteger personAge;
}

- (id)initWithName:(NSString *)name andAge:(NSInteger)age;
- (void)print;
@end

@implementation Person

- (id)initWithName:(NSString *)name andAge:(NSInteger)age{
    personName = name;
    personAge = age;
    return self;
}

- (void)print{
    NSLog(@"Name: %@", personName);
    NSLog(@"Age: %ld", personAge);
}

@end

@interface Employee : Person

{
    NSString *employeeEducation;
}

- (id)initWithName:(NSString *)name andAge:(NSInteger)age 
  andEducation:(NSString *)education;
- (void)print;

@end


@implementation Employee

- (id)initWithName:(NSString *)name andAge:(NSInteger)age 
  andEducation: (NSString *)education
  {
    personName = name;
    personAge = age;
    employeeEducation = education;
    return self;
}

- (void)print
{
    NSLog(@"Name: %@", personName);
    NSLog(@"Age: %ld", personAge);
    NSLog(@"Education: %@", employeeEducation);
}

@end


int main(int argc, const char * argv[])
{
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];        
    NSLog(@"Base class Person Object");
    Person *person = [[Person alloc]initWithName:@"Raj" andAge:5];
    [person print];
    NSLog(@"Inherited Class Employee Object");
    Employee *employee = [[Employee alloc]initWithName:@"Raj" 
    andAge:5 andEducation:@"MBA"];
    [employee print];        
    [pool drain];
    return 0;
}

上面的代碼編譯和執(zhí)行時，它會產(chǎn)生以下結果：

2013-09-22 21:20:09.842 Inheritance[349:303] Base class Person Object
2013-09-22 
            
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