DESIGNING J2ME APPLICATIONS in Java

Paint QR-Code in Java DESIGNING J2ME APPLICATIONS

As with any system architecture, there are tradeoffs to consider. This is the art of architecture. Creating an architecture that includes J2ME is no exception. Most likely, there will be a large number of devices involved, possibly different devices types and manufacturers, varying network capabilities, and data storage capabilities. Here are some things to consider when creating J2ME applications. Techniques for addressing some of these issues are discussed in part 4.

The design of J2ME applications should include an understanding of the devices you intend to support. This understanding allows the appropriate profiles to be included in the design and implementation of applications. Additionally, you should have some understanding of the unique capabilities and constraints of each device. This is a good idea even if only one profile is supported. You must remember that a single cell phone application could be used on many different manufacturer s phones. If you plan to support devices with a mixture of capabilities, such as cell phones, pagers, and PDAs, you may want to provide capabilities specific to each device. For example, some pagers have a full keypad where cell phones have a 10-digit keypad. PDAs usually have wider screens than cell phones and pagers. Some PDAs are even powerful enough to run a small-footprint relational database. Another important consideration is how portability factors into your application requirements, and your organization. As discussed previously, the write once, run anywhere promise does not come automatically with J2ME. Is this a necessary requirement for your application Is it practical You will also want to consider how the applications will be delivered to the device and what kind of network capabilities they will need to operate. Different devices may require different network connectivity infrastructures. For example, does your wireless service provider allow the device to connect to the Internet or will you be stuck on their server How much does it cost per minute to be connected How much data must be transferred over the network connection Is this too much for a 19.6 kbps or 9600 bps connection Will the application run transiently or will it be installed on the device Will there be a combination of installed and transient applications The tradeoff between how much data can be downloaded and how much data can be stored is often a key architectural decision. Some devices must download a fair amount of their operational data simply because they do not have the space to store the data locally. Some devices may not even have the ability to store data. Of course, requiring data downloads to operate an application means the device must have a connection. On the other side of the coin, applications that store data locally on the device may have to deal with data synchronization issues between the device and the server. You will also want to address usability issues with certain devices. For example, what happens when someone is using your stock application on a cell phone and he or she suddenly gets a phone call Can the user easily suspend the application Is this automatically done by the device

The J2ME architecture defines configurations to address the horizontal needs of the J2ME space. The J2ME Virtual Machines are tightly coupled to the configurations that define them. Profiles fill in the gaps left by configurations and implement specific capabilities for a family of devices. Profiles tend to address vertical aspects of the J2ME space, such as specific device capabilities and limitations, or they encapsulate a set of APIs that address a specific market or technology need. For compatibility between devices, manufacturers must implement the entire profile specification. This allows applications that conform to the profile to run on any device that implements the profile. Finally, it is important to understand that a device may support one or more profiles on a single configuration. With a solid understanding of how J2ME is put together and what options exist for developing applications, you are ready to try out some of this. The next few chapters cover creating and deploying J2ME applications.