使用copy再次实现Circle类，保证不能有内存泄漏问题

 #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

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

 @interface Circle : NSObject<showOn>{
     MyPoint* point;
     int radius;
 }
 @property (nonatomic,copy)MyPoint* point;
 @property (nonatomic,assign)int radius;
 -(id)initWithPoint:(MyPoint* )_p andRadius:(int)_r;
 -(id)initWithPoint:(MyPoint *)_p;

 @end

 #import "Circle.h"

 @implementation Circle
 @synthesize point;
 @synthesize radius;

 -(id)initWithPoint:(MyPoint *)_p andRadius:(int)_r{
     if(_r==)
     {
         radius=;
     }
     if(_p==nil)
         return nil;
     if(self=[super init])
     {
         if(point!=_p)
         {
             if(point)
                 [point release];
             point =[[MyPoint alloc]initWithX:_p.x andY:_p.y];
         }

     }
         radius=_r;
         return self;
 }

 -(id)initWithPoint:(MyPoint*)_p{
     self=[self initWithPoint:_p andRadius:];
     return self;
 }

 -(void)printOn{
     NSLog(@"point(x,y) = (%d,%d),radius = %d",point.x,point.y,radius);
 }

 -(void) dealloc{
     [point release];
     [super dealloc];
 }

 @end