Eclipse: Java compiler level and project facet mismatch

Symptom: In eclipse IDE, in the 'Problems' view, you see the error
"Java compiler level does not match the version of the installed Java project facet"

Cause: You may have set the Java Compiler Level different from the Java version shown in the Project Facets.

The Java compiler level is accessed by:
- Right mouse click on Project
- Select Properties->Java Compiler
- and set the version in the dialog provided.

The Java Facet version is accessed by:
- Right mouse click on Project
- Select Properties->Project Facets
- You can click on the 'Java' version column

You have two options to fix the issue:
1- Manually make sure the two versions match.
2- Use the IDE's help as follows:
- Right mouse click on the error in the 'Problems' view
- Select the 'Quick Fix' menu item from the pop-up menu
- Select the right compiler level in the provided dialog and click 'Finish'.

refer:
http://codewriterstips.blogspot.in/2009/03/eclipse-java-compiler-level-and-project.html