Java makes it possible to write many kinds of applications that have been imagined for years , but haven't been practical before. Many of these applications would require too much processing power if they were entirely server-based; Java moves the processing to the client, where it belongs. Other application types require extreme portability and some guarantee that the application can't do anything hostile to its host. While Java's security model has been criticized (and yes, some bugs have been found), it's a quantum leap beyond anything that has been attempted in the past and an absolute necessity for the mobile software we will want to write in the future.
Most of this book describes the fairly low-level APIs needed to write the kinds of programs discussed above. Some of these programs have already been written. Others are still only possibilities. Maybe you'll be the first to write them! This chapter has just scratched the surface of what you can do when you make your Java programs network aware. You're going to come up with ideas others would never think of. For the first time, you're not limited by the capabilities that other companies build into their browsers. You can give your users both the data you want them to see and the code they need to see that data at the same time.