main.m

#import <Foundation/Foundation.h>
#import "Person.h"

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

    @autoreleasepool {
        Person *person = [[Person alloc] init];
        
        person.age = 10; // 等效于[person setAge:10];
        
        int age = person.age; // 等效于int age = [person age];
        
        NSLog(@"age is %i", age);
        
        [person release];
    }
    return 0;
}

person.h

#import <Foundation/Foundation.h>

@interface Person : NSObject {
    int _age;
}

- (void)setAge:(int)age; // 方法名是setAge:
- (int)age; // 方法名是age

// 方法名是setAge:andNo:
// - (void)setAge:(int)newAge andNo:(int)no;
@end

person.m

#import "Person.h"

@implementation Person
						
- (void)setAge:(int)age {
    NSLog(@"调用了setAge方法：%i", age);
    _age = age;
    
    // 这是错误的写法，会导致死循环，无限调用set方法
    // self.age = newAge;// [self setAge:newAge];
}

- (int)age {
    NSLog(@"调用了age方法：%i", _age);
    
    return _age;
}
@end