What operating system was java developed?

Java

Java was developed to be run on any OS. The existence of the Java Virtual Machine means that only the JVM has to be ported to different platforms, so Java source code can be run on any of those platforms without any change.

(If the question was asking what system Java was developed on, then I don't know for sure. But since it was developed at Sun Microsystems, one could safely assume it was written in some version of Solaris.)