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==0)
        x=1;
    if(_y==0)
        y=1;
    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==0)
    {
        radius=1;
    }
    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:10];
    return self;
}

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

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

@end