If you are employeed now as a Java programmer, it is a good idea for you to take Sun's test. If you want to get some certificates for job hunting, I advise you against taking such exams. Unless you have somem years of Java programming experiences, you have little hope to pass Sun's developer certificate test. Even you have held 3 certificates, you still need to answer various kinds of questions . It seems to me that few companies make a job offer on the basis of some certificates.
I suggest you study Sun's blueprint book, run Sun's pet store demo, investigate Apache's struts, read 50 articles from www.javaworld.com,...
These things are more helpful. Trust me, I am a Java programmer.