IOS atomic与nonatomic，assign,copy与retain的定义和区别

http://blog.csdn.net/mars2639/article/details/7352540

https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/EncapsulatingData/EncapsulatingData.html#//apple_ref/doc/uid/TP30001163-CH17-SW1

http://blog.sina.com.cn/s/blog_63b4ee0d0101gi14.html

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

- (void) setName:(NSString*) str

{

[str retain];

[name release];

name = str;

}

- (void)setName:(NSString *)str

{

id t = [str copy];

[name release];

name = t;

}