Fixed Ubuntu apt-get update issue

Problem :
    root@ubuntu:~# apt-get upgrade
    Reading package lists... Done
    Building dependency tree
    Reading state information... Done
    You might want to run 'apt-get -f install' to correct these.
    The following packages have unmet dependencies:
         default-jre : Depends: default-jre-headless (= 1:1.6-43ubuntu2) b
    E: Unmet dependencies. Try using -f.

Fixed :
   using following command, force to dist-upgrade
   apt-get -o APT::Immediate-Configure=false -f dist-upgrade