Main.m

#import <Foundation/Foundation.h>
#import "Piano.h"
#import "Violin.h"
#import "Actor.h"/*乐器（Instrument）分为：钢琴(Piano)、小提琴(Violin)。各种乐器的弹奏（ play ）方法各不相同。演奏家可以使用各种乐器。
*/int main(int argc, const char * argv[])
{//创建演奏者和乐器Actor *actor = [[Actor alloc] init];Piano *piano = [[Piano alloc] init];Violin *violin = [[Violin alloc] init];int cmd;NSLog(@"请输入需要使用的乐器：");scanf("%d",&cmd);if (cmd == 1) {[actor playWithInstrument:piano];}else if (cmd == 2) {[actor playWithInstrument:violin];}else {NSLog(@"输入有误");}return 0;

Actor.h

//使用乐器演奏的方法
- (void)playWithInstrument:(Instrument *)instrument;

Actor.m

//使用乐器演奏的方法
- (void)playWithInstrument:(Instrument *)instrument {[instrument play];}

Instrument.h

@interface Instrument : NSObject//演奏
- (void)play;

Instrument.m

//演奏
- (void)play {NSLog(@"乐器演奏");}

Piano.m

//演奏
- (void)play
{NSLog(@"钢琴演奏");}

Violin.m

//演奏
- (void)play {NSLog(@"小提琴演奏");}