Java can be obtained in one of two flavors: Java Runtime Environment (JRE) or Java Development Kit (JDK). Unless you do programming in Java, JRE is usually sufficient for running programs and applets written in Java. JRE is also included in JDK so there is no need to install both. There are two main flavors of Java that we have support for Oracle Java and OpenJDK. For the Java6 spec OpenJDK was not the same codebase and had some issues with some code that would run in the normal Oracle Java6 JVM. The Java7 versions of OpenJDK is much closer if not the same codebase for Oracle Java and OpenJDK.
Note: Support for Sun JDK 1.6.0 has ended and we will be purged from UMIACS supported systems in March 2013 due to many security vulnerabilities. This does not impact the OpenJDK 1.6.0 versions as they are still maintained at this point.
The default Java on the system currently Sun Java 1.6.0 which will be replaced by Oracle Java 1.7.0 in March 2013. We additionally have available OpenJDK 1.6.0 which is shipped and is currently at version 1.6.0 on RHEL5 and RHEL6.
The default Java on Ubuntu systems is OpenJDK 1.6.0 and 1.7.0 is available in the default repositories.
For PCs, you may send a request to staff to have JRE or JDK installed on your machine.