Best way to generate a unique ID in java

Question

What is the best way to generate a unique ID in java. People generally use

String id = System.currentTimeMillis+ someStaticCounter;

But this a

Answer 1

How about UUID: http://java.sun.com/j2se/1.5.0/docs/api/java/util/UUID.html#randomUUID%28%29

Answer 2

UUID.randomUUID()