Error: The method onItemSelected(String) of type ItemListActivity must override a superclass method

It MAY BE happen if you new a project using the new Android SDK Revision 20: Eclipse complain with errors of:
- The method onItemSelected(String) of type ItemListActivity must override a superclass method
- The method onItemSelected(String) of type new ItemListFragment.Callbacks(){} must override a superclass method

Checking the updated System requirements of Android SDK, only JDK 6 is officially supported:

To fix it: correct Compiler compliance level to 1.6.

- Right click your project, select Properties.

-  Select Java Compiler tab, change Compiler compliance level to 1.6.

- Alternatively, you  can click Window -> Preferences, then select Java -> Compiler to change Compiler compliance level to 1.6 for the whole workspace.

Then clean and re-build. Now fixed with 0 errors.