JAVA Error:The project was not built since its build path is incomplete. Cannot find the class file for java.util.Map$Entry.....

　　今天，学习Netty框架时遇到error:Description Resource Path Location Type:The project was not built since its build path is incomplete. Cannot find the class file for java.util.Map$Entry. Fix the build path then try building this project NettyTest Unknown Java Problem

　　于是，百度了一番，发现应该是JDK版本问题，或许我用的Netty框架的jar包不兼容当前版本的JDK，我试着修改当前使用的JDK版本。

　　果然，解决了，其实好多类似的问题都是这原因引起的，都可以试着这样解决，再次我临时不能把这些问题列举出来。