This is usually because your JDK version is not set, or set There is inconsistency.
1. First check window-> preferences-> Java-> Installed JRE version of the compiler and are consistent inconsistent consistent set it. If you see an error this time the second step.
2. On the Project Right -> properties-> Java Build Path-> Libraries check which version of the JRE with JRE that you set in the first step are the same, it should be inconsistent, then delete the original JRE then add the Add Library the first step in the Library settings, click OK to not being given the friends ~
Reproduced in: https: //www.cnblogs.com/ericsun/archive/2011/10/24/2222549.html