http://blog.csdn.net/smile_juan/article/details/8479200
Here is the solution.
It's similar to the link I found. http://dev-answers.blogspot.com/2009/06/eclipse-build-errors-javalangobject.html
1: Go to properties of project with the build error (right click > Properties)
2: View the "Libraries" tab in the "Build Path" section
3: Find the "JRE System Library" in the list (if this is missing then this error message is not an eclipse bug but a mis-configured project)
4: Remove the "JRE System Library"
5: Hit "Add Library ...", Select "JRE System Library" and add the appropriate JRE for the project (eg. 'Workspace default JRE')
6: Hit "Finish" in the library selection and "OK" in the project properties and then wait for the re-build of the project
7: Hopefully the error will be resolved ...