玄学eclipse ,突然所有文件报错，然后，ctrl+a, ctrl+x, ctrl+v就好了

突然，eclipse报错了，所有工程文件都标记叉号：

Syntax error on token "package", byte expected

Syntax error on token "import", throw expected

Illegal modifier for the local class myconfigurations; only abstract or final is permitted

然后挨个打开，然后，ctrl+a, ctrl+x, ctrl+v就好了，why?