The wrapper class for SCJP is an important topic that is taken up in training for the Java Programmer exams. There are two Java Programmer exams that are concerned with the wrapper class: the SCJP (Sun Certified Java Programmer) Exam CX-310-025 (which deals with Java 2 Platform 1.2) and the SCJP Exam CX-310-035 (which deals with Java 2 Platform 1.4.)
In the SCJP Exam CX-310-035, more questions dealing with wrapper classes are introduced. So expect to be asked to give detailed answers about wrapper classes. SCJP accredited people who have taken Exam CX-310-025 before and passed are advised to learn about and take the SCJP Exam CX-310-035 as well so that their SCJP status stays up to date.
In the same way that some question categories have been eliminated from SCJP Exam CX-310-035 (also called SCJP Exam 1.4), the creators of the exam have decided to emphasize wrapper classes more to assure that exam takers get a deeper appreciation of wrapper classes in the SCJP accreditation process and application.
When studying about wrapper classes, you may find it under the chapter on Fundamental Classes in the java.lang Package. Expect exam questions to revolve around why wrapper classes are vital to Java, when certain wrapper classes should be chosen due to perceived behavior stipulations, and what the result of code fragment execution should be when a certain wrapper class is used. You may also be asked to determine and enumerate certain methods in writing code based on specific wrapper classes.