为MYPoint类写一个分类

 #import <Foundation/Foundation.h>
 //xieyi
 @protocol showOn
 @required
 -(void)printOn;
 @end
 // lei
 @interface MyPoint : NSObject<showOn,NSCopying>{
     int x;
     int y;
 }
 @property (nonatomic,assign)int x,y;
 -(id)initWithX:(int)_x andY:(int)_y;
 @end
 // leibie fenlei
 @interface MyPoint(MoveSet)
 
 -(void)moveToX:(int)_x andY:(int)_y;
 
 @end
 
 #import "MyPoint.h"
 
 @implementation MyPoint
 @synthesize x,y;
 
 -(id)initWithX:(int)_x andY:(int)_y{
     if(_x==)
         x=;
     if(_y==)
         y=;
     x=_x;
     y=_y;
     return self;
 }
 
 -(id)copyWithZone:(NSZone *)zone{
     MyPoint* newPoint=[[MyPoint allocWithZone:zone] initWithX:x andY:y];
     return newPoint;
 }
 
 -(void)printOn{
     NSLog(@" x = %d , y = %d ",x,y);
 }
 
 @end
 
 @implementation MyPoint(MoveSet)
 
 -(void)moveToX:(int)_x andY:(int)_y{
     x=_x;
     y=_y;
 }
 
 @end