You probably noticed since you’ve upgraded to MacOS X Yosemite 10.10 that Java application fail yo start and the following message appear on your screen :
To view this web content, you need to install the Java Runtime Environment.
If you had Java JRE 1.7.x before the OS upgrade, then be aware that version prior 1.8.x are not compatible/supported with OSX 10.10. I would suggest removing the old version using the terminal and the following command :
sudo rm -fr /Library/Internet\ Plug-Ins/JavaAppletPlugin.plugin
Then, download/install the latest Java JRE version from Oracle Web site [link]
If you are still experiencing that issue after this process (like I had with one of my computer), then try downloading and installing Java JDK 1.8.x (Development Kit) [link] instead, it solved the issue for me.