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;
}
IOS atomic与nonatomic，assign,copy与retain的定义和区别
原文：http://www.cnblogs.com/ian-fix/p/4174137.html