欢迎来到Doc100.Net免费学习资源知识分享平台!
您的位置:首页 > 程序异常 >

why inner class can access only final variable

更新时间: 2014-01-05 02:25:13 责任编辑: Author_N1

 

why inner class can access only final variable?

Local classes can most definitely reference instance variables. The reason they cannot reference non final local variables is because the local class instance can remain in memory after the method returns. When the method returns the local variables go out of scope, so a copy of them is needed. If the variables weren’t final then the copy of the variable in the method could change, while the copy in the local class didn’t, so they’d be out of synch.

Anonymous inner classes require final variables because of the way they are implemented in Java. An anonymous inner class (AIC) uses local variables by creating a private instance field which holds a copy of the value of the local variable. The inner class isn’t actually using the local variable, but a copy. It should be fairly obvious at this point that a “Bad Thing”™ can happen if either the original value or the copied value changes; there will be some unexpected data synchronization problems. In order to prevent this kind of problem, Java requires you to mark local variables that will be used by the AIC as final (i.e., unchangeable). This guarantees that the inner class’ copies of local variables will always match the actual values.

上一篇:上一篇
下一篇:下一篇

 

随机推荐程序问答结果

 

 

如对文章有任何疑问请提交到问题反馈,或者您对内容不满意,请您反馈给我们DOC100.NET论坛发贴求解。
DOC100.NET资源网,机器学习分类整理更新日期::2014-01-05 02:25:13
如需转载,请注明文章出处和来源网址:http://www.doc100.net/bugs/t/9570/
本文WWW.DOC100.NET DOC100.NET版权所有。