zoukankan      html  css  js  c++  java
  • Objective-C Inheritance

    One of the most important concepts in object-oriented programming is that of inheritance. Inheritance allows us to define a class in terms of another class which makes it easier to create and maintain an application. This also provides an opportunity to reuse the code functionality and fast implementation time.

    When creating a class, instead of writing completely new data members and member functions, the programmer can designate that the new class should inherit the members of an existing class. This existing class is called the baseclass, and the new class is referred to as the derived class.

    The idea of inheritance implements the is a relationship. For example, mammal IS-A animal, dog IS-A mammal, hence dog IS-A animal as well and so on.

    Base & Derived Classes:

    Objective-C allows only multilevel inheritance, i.e., it can have only one base class but allows multilevel inheritance. All classes in Objective-C is derived from the superclass NSObject.

    @interface derived-class: base-class

    Consider a base class Person and its derived class Employee as follows:

    #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;
    }

    When the above code is compiled and executed, it produces the following result:

    2013-09-22 21:20:09.842 Inheritance[349:303] Base class Person Object
    2013-09-22 21:20:09.844 Inheritance[349:303] Name: Raj
    2013-09-22 21:20:09.844 Inheritance[349:303] Age: 5
    2013-09-22 21:20:09.845 Inheritance[349:303] Inherited Class Employee Object
    2013-09-22 21:20:09.845 Inheritance[349:303] Name: Raj
    2013-09-22 21:20:09.846 Inheritance[349:303] Age: 5
    2013-09-22 21:20:09.846 Inheritance[349:303] Education: MBA

    Access Control and Inheritance:

    A derived class can access all the private members of its base class if it's defined in the interface class, but it cannot access private members that are defined in the implementation file.

    We can summarize the different access types according to who can access them in the following way: 

    A derived class inherits all base class methods and variables with the following exceptions:

    • Variables declared in implementation file with the help of extensions is not accessible.

    • Methods declared in implementation file with the help of extensions is not accessible.

    • In case the inherited class implements the method in base class, then the method in derived class is executed.

  • 相关阅读:
    (转).NET 多线程编程
    [WAP]WML学习笔记总结
    [计划]2010年1月的工作学习计划
    [计划]11月&12月学习与工作计划
    [HTTP]HTTP协议学习总结第一弹:RFC2616初读总结
    [培训总结]海量服务培训总结
    [随想]忙碌的2010
    Android电源管理
    Android 1.5: 飞行模式分析
    android JNI 调用
  • 原文地址:https://www.cnblogs.com/xujinzhong/p/8514918.html
Copyright © 2011-2022 走看看