Code:
root@opus:~# sudo update-alternatives --install "/usr/share/java" "java" "/usr/share/java/jdk1.7.0/bin/java" 1
update-alternatives: warning: forcing reinstallation of alternative /usr/share/java/jdk1.7.0/bin/java because link group java is broken.
update-alternatives: warning: not replacing /usr/share/java with a link.
Please help