8.4. Using a Subset of the J2SE
For example, I started using the java.text.DateFormat class, until I remembered that the java.text package is not available (right now) in the GWT API. So for that particular application, I had to rely on the java.util.Date functionality in lieu of creating my own module for the java.text classes.
Many of the classes that Java programmers use quite often from java.lang, however, are mirrored in the GWT. The GWT has included ArrayList, HashMap, and HashSet, for instance. Typically, you will find that enough GWT API classes exist to help you accomplish your task.
The following API web pages describe which classes the GWT makes available in java.lang and java.util.