Cannot find the class file for java.lang.Object

Check this if it works:

There is a problem with your java repositories. I guess..:

goto Help>Install New Software> Click on Add Button .

on popup:

Name: ADT

Location:https://dl-ssl.google.com/android/eclipse

Install all the available softwares in the list. This may work.

Have a good day!!!

Right click on Project--> Properties, Java Build Path.

Check whether you have JRE installed. If installed click on EDIT and check whether its pointing to correct location