aka. MacOS X 10.10. Release in October 2014 as a free upgrade for people with existing MacOS X installations on compatible hardware.
Changes to the user interface are readily visible, but there have also been modifications to the underlying infrastructure.
There does not seem to be a java installed by default in Yosemite. If you have applications that need java this link may meet your needs.
From what we have observed, if you use the Java 6 runtime in a 10.9/8 environment, updating to Yosemite removes this. When you try to run something that expects Java, then you will see an alert that may direct you to the download indicated above.
Oracle has a FAQ on what java 7 or 8 will install on OS X Yosemite, There are links to the versions for both Java 7 and 8.
Mathworks reports that Matlab 2014b will work with OS X 10.10 Yosemite, but has also provided patches for earlier versions of Matlab. Some of them are available from smb:\scidrive.uoa.auckland.ac.nzsit$softwarematlabYosemite Patches.
Matlab 2014b is now available in smb:\sit-buildPACKAGESMathWorksMATLABisosR2014b_maci64.iso .
Moving to OS X 10.10 may break printing to direct printers such as those used in some departments including direct CAPS Printers.