setter方法

写一个setter方法用于完成@property(nonatomic, strong)NSString *name,
写一个setter方法用于完成@property(nonatomic, copy)NSString *name

- (void)setName:(NSString*)str //retain
　{
　　[str retain];
　　[_name release];
　　_name = str;
　}
- (void)setName:(NSString *)str //copy
　{
　　id t = [str copy];
　　[_name release];
　　_name = t;
　}