未调用描述方法

description 方法打印一些数据,然后AFAIK, description method toString 在java中..但是 未调用我创建的方法

请看一下下面的代码,让我知道为什么

#import <Foundation/Foundation.h>

@interface Person : NSObject {
    int age;
    int weight;
}

-(void) setAge:(int) age;
-(void) setWeight: (int) weight;

-(int) getAge;
-(int) getWeight;

-(NSString *) description;

@end

人.m

#import "Person.h"

@implementation Person

-(void) setAge:(int) a {
    age = a;
}

-(void) setWeight:(int) w {
    weight  = w;
}

-(int) getAge {
    return age;
}

-(int) getWeight {
    return weight;
}

-(NSString *) description {
    NSString *desc = @("my age is: %i and my weight is: %i", age, weight);
    NSLog(@"%@", desc);
    return desc;
}
@end

:

#import <UIKit/UIKit.h>
#import "AppDelegate.h"
#import "Person.h"

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

        Person *me = [[Person alloc] init];

        [me setAge:20];
        [me setWeight:55];

        NSString *desc = [me description];
        NSLog(@"%@", desc);

        return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
    }
}