跟进：类方法和实例方法之间的区别？

问题描述：

这是（用户）micmoo对What is the difference between class and instance methods?的回应的后续问题。跟进：类方法和实例方法之间的区别？

如果我将变量numberOfPeople从静态更改为类中的局部变量，我将numberOfPeople设置为0.我还在每次增加变量后添加了一行以显示numberOfPeople。只是为了避免任何混乱，我的代码如下：

// Diffrentiating between class method and instance method 

#import <Foundation/Foundation.h> 


// static int numberOfPeople = 0; 

@interface MNPerson : NSObject { 
    int age; //instance variable 
    int numberOfPeople; 
} 

+ (int)population; //class method. Returns how many people have been made. 
- (id)init; //instance. Constructs object, increments numberOfPeople by one. 
- (int)age; //instance. returns the person age 
@end 

@implementation MNPerson 

int numberOfPeople = 0; 
- (id)init{ 

    if (self = [super init]){ 
     numberOfPeople++; 
     NSLog(@"Number of people = %i", numberOfPeople); 
     age = 0; 
    }  
    return self; 
} 

+ (int)population{ 
    return numberOfPeople; 
} 

- (int)age{ 
    return age; 
} 

@end 

int main(int argc, const char *argv[]) 
{ 
    @autoreleasepool { 


    MNPerson *micmoo = [[MNPerson alloc] init]; 
    MNPerson *jon = [[MNPerson alloc] init]; 
    NSLog(@"Age: %d",[micmoo age]); 
    NSLog(@"Number Of people: %d",[MNPerson population]); 
} 

}

输出：

在初始块。人数= 1在init块中。人数= 1年龄：0人数：0

案例2：如果您将执行中的numberOfPeople更改为5（说）。输出仍然没有意义。

非常感谢您的帮助。

您不更改类型，而是创建新变量。 – Dustin 2012-08-09 17:22:42

非常感谢达斯汀！ – 2012-08-09 20:35:52

答

您正在隐藏实例级别为numberOfPeople的全球声明的numberOfPeople。将其名称之一改为其他名称以避免此问题

非常感谢Dan！ – 2012-08-09 20:34:53

跟进：类方法和实例方法之间的区别？

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