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For more information on this, take a look at:
Java for OS X 2013-004
Please quit any web browsers and Java applications before installing this update.
See http://support.apple.com/kb/HT5717 for more details about this update.
See http://support.apple.com/kb/HT1222 for information about the security content of this update.
Best of luck,
to install java on your mac go to the following website:
after you have the download, go into the finder window and your downloads, find the one for java and doubleclick it to finish the installation of it
then go to this website to make sure it's properly activated:
if it's not that website will activate it and then just quit the browser and reopen it for the change to take affect and you should be fine.