Ubuntu: OpenJDK 8 - Unable to locate package

So I just installed Ubuntu, and this is my first time working in a Linux environment, so bear with my noobishness here.

Anyway, I downloaded the Java 8 JDK directly from Oracle, but I understand there's also an OpenJDK for Java 8 as well. I have two questions.

1. What is the difference between the Oracle version and OpenJDK. Pros/Cons?

2. When I try and get OpenJDK 8, I can't. I'm pasting the terminal command and the error message I get here, hoping for advice. Again, very new to Linux, been on my first Linux distro ever for less than an hour here at this point.

   user@computer:~/Java$ sudo apt-get install openjdk-8-jdkReading package lists... DoneBuilding dependency tree       Reading state information... DoneE: Unable to locate package openjdk-8-jdk

Any help would be appreciated. In the meantime, I'm just gonna use the Oracle package. Thanks.

Edit:

So, now I have a new problem. I installed OpenJDK 7, it came with Maven and just installed before I realized I was getting a two-for-one deal. Now I have JDK 7, and Eclipse, and Maven, and they're all working, but I'm stuck on JDK 7 rather than 8.

I saw that there's a link below, I intend to check it out in the morning, it's 2am and I'm tired right now. Any other advice for this new issue would be appreciated, otherwise I will definitely be checking out that link first thing in the morning.