Have you performed any troubleshooting steps? If so, you like to share them with us?
Did you select 'Safari's 'Safari, Preferences...' menu item, then the 'Security' icon on the toolbar, and then verify that the 'Enable Java' check box had a check mark present?
Are you trying to view a Java based web page?; or, are you writing Java code - and for some reason it is not viewable?
Whether your problem is web page or written code based, did you try to view the desired material with other Macintosh web browsers?