In Eclipse's menu toolbar, click on "Project" then click on "Properties". Your project properties window should appear. On the left-hand side tree, click on "Java Build Path". There will be 4 tabs on the right-hand side window. Click on "Libraries". In my configuration, java.lang.Object is in the rt.jar provided by the JRE. Make sure you have a jar that has java.lang.Object in your libraries tab and that the jar exists (just in case you upgraded your JRE or something like that).