Programming Wireless Devices with the Java2 Platform

3.2 Target Devices

Potential target devices for the Mobile Information Device Profile (MIDP) include two-way communication devices such as cellular telephones, two-way pagers, and wireless personal organizers. The Connected, Limited Device Configuration (CLDC) can additionally be used to support other kinds of devices such as point-of-sale terminals, barcode scanners, inventory control devices, audio/video equipment, home appliances, and device controllers (for routers, sensors, vending machines, engines, and so forth). In general, CLDC is intended to be applicable to any resource-constrained device that might benefit from a portable, low-cost application development environment that supports secure, dynamic downloading of third-party applications.^[2]

^[2] Note that CLDC defines only general-purpose APIs, so additional APIs and/or J2ME profiles are typically necessary to address the specific needs of each device category.

The characteristics of the CLDC and MIDP target devices are summarized in Figure 3.2. The technical hardware and software requirements of CLDC and MIDP target devices are defined in detail later in this chapter.

The user interaction models of CLDC and MIDP target devices vary significantly. Consider, for example, how a user interacts with today's crop of mobile information devices.

The most common example is that of "one-handed" operation. Devices of this type are typical cellular phones with small LCD displays and a standard ITU-T telephone keypad (containing at least the keys 0?, *, and #). Users interact with this type of device with one hand, usually with their thumb only. With devices of this type, smaller is better, so these devices typically have a very limited display.

Other mobile information devices are operated in "two-handed mode." These devices have a small, conventional "QWERTY" keyboard. Data entry for these devices is much like using a PC, although due to the small size, touch typing can be problematic; consequently, many devices in this category are operated by two thumbs rather than ten fingers. Given that a QWERTY keyboard takes up more space than a telephone keypad, the display in these devices is usually larger than that found in a normal cellular phone.

As a final example of user interaction models, consider a device that depends on a touch screen. These devices primarily interact with the user by having a simple, consistent, and well-designed menu system. In addition, these devices might depend on handwriting recognition or a virtual keyboard for user-input text. Given that text input is commonly done via a stylus, these devices typically have larger LCD screens梚n fact, often much larger than the other two types of devices discussed.

Both CLDC and MIDP are designed to cater to all the different usage models presented in Figure 3.3, and consequently the CLDC and MIDP specifications make minimal assumptions about user interaction models of the target devices.