延展性，实现方法的私有化

//Study.m文件声明

#import <Foundation/Foundation.h>

@interface Study : NSObject

-(void)study; 

@end

//Study.h文件实现

#import "Study.h"

@interface Study ()//偷偷声明

-(void)playLOL;

-(void)playCF;

@end

@implementation Study

-(void)study

{
    NSLog(@"我正在学习");

    [self playCF];

    [self playLOL];

}

-(void)playLOL//延展1

{
    NSLog(@"我同样在玩LOL");
}

-(void)playCF//延展2

{
    NSLog(@"我还在玩CF");
}

@end

 //main.m文件中

Study *xiaoming=[[Study alloc]init];

[xiaoming study];

//

2015-11-10 18:53:47.972 test[7322:112328] 我正在学习
2015-11-10 18:53:47.972 test[7322:112328] 我在玩CF
2015-11-10 18:53:47.972 test[7322:112328] 我在玩LOL