I try entering this to install java JDK
sudo apt-get install openjdk-7-jdk
It responds with this
Reading package lists... Done
Building dependency tree... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
openjdk-7-jdk : Depends: openjdk-7-jre (= 7u55-2.4.7-1ubuntu1~0.12.04.2) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
I have no idea how to deal with this.
sudo apt-get update
first?