Note that Netscape comes also with Java bundled with its software. Navigator can't work without it...
If you have Netscape, you may try to go to the upgrade page to download Netscape 7, which will reinstall Java on your system. If Netscape 7 works, Java is also fine...
(Note that Netscape will propose to download Java even if you have it. you should say yes to reinstall the Java JRE version 1.3.1)