After updating to Yosemite you may receive a message saying you need to install the legacy Java SE 6 Runtime. The cause of this problem seems to be with Java.
Mac OSX Version 10 is confusing in the same way that Y2k was. The digit rolled over, meaning that installers treat the .10 as a 1, rather than a 10. This means that many system installers, including Java, will not allow newer software to download. Java is pretty important though, so here are a few work arounds.
Try installing the newest version of Java by going to www.java.com. In case this does not work, please install an older version of Java from the Apple website: http://support.apple.com/kb/DL1572?viewlocale=en_US&locale=en_US Please note however, that Java 6 is outdated and may pose security risks if you allow your browser to use Java. You can have Java 6 and 8 on your machine.