Hi Pankaj,
The problem you are facing is due to lower version of java being specified in your facet settings.
Probable Solution:
Goto project properties -> Select Project Facets -> Check the Java version, if it is other than java 5.0 then click on Add/Remove Project Facets.
A new pop-up will open select "Facets Project" from the configurations dropdown.
Now you will see a Project Facet named "Java". select the checkbox and change the version to 5.0 and click finish.
Clean build your workspace.
Hope the above solution works for you. All the best.
Cheers
Javish