Ok, hold on one second. I have a feeling that what you really are asking is "Is the Nexus One J2ME enabled. J2ME is a java implementation developed by Sun that is available on many phones. However, Android is not a J2ME implementation. Google basically made up their own Java implementation.
So if you are looking to use games or other apps that are J2ME, these will not work on the Nexus One, or any other Android phone that I am aware of.
The problem is that the term "Java" is a bit ambiguous when used by itself. Android apps are built using the Java programming language, but Android does not provide a Java Runtime Environment for Android that is compatible with Sun's standard and implementation. Hope that helps.