Java 2 Micro Edition Architecture

 In mid-1999, J2ME was introduced to developers of intelligent wireless devices and small computing devices who need to incorporate cross-platform functionality in their products.

• J2ME technology provides tools to build an industrial-strength Java application designed to run on a small computing device.
• J2ME application makes use the same basic programming constructs as used in a J2SE application. But, some routines commonly used in a J2SE application must be modified or excluded from a J2ME application.

Expectations of Consumers of Mobile and Small Computing Devices include the following:

• Quick response time
• Compatibility with companion services
• Full-featured applications  
• Software and capabilities found on their desktop and laptop computers to be available on their cell phones and Personal Digital Assistant

A Change in the Client/Server Technology:

• A thick client is front-end software that contains the logic to handle a sizable amount of data processing for the system (Figure 1-3). 

• A thin client is front-end software that depends on back-end software for much of the system processing.  J2ME promotes thin client for the development of its applications for small computing devices (Figure 1-4)

An Order Processing Application:

An order processing using wireless device has the following steps:

• Handles user interactions by displaying an electronic form on the screen
• Collects user input
• Processes the input, and 
• Displays results on the screen

At the front-end, this process can be done using wireless device in two steps: 

• The software performs a simple validation process to assure that all fields on the form contain information.
• The order is transmitted to the back-end system. 

At the back-end system, the actual processing takes place as follows:

• Handles adjusting account balances and other steps involved in processing the order. 
• A confirmation notice is returned by the back-end system to the wireless device, which displays the confirmation notice on the screen (Figure 1-5)

J2ME Architecture:

J2ME architecture doesn’t replace the operating system of a small computing device. Instead, J2ME architecture consists of layers located above the native operating system, collectively referred to as the Connected Limited Device Configuration (CLDC).

The CLDC, which is installed on top of the Operating System, forms the run-time environment for small computing devices.

The J2ME architecture comprises three software layers (Figure 3-1):

• The first layer is the configuration layer that includes the Java Virtual Machine (JVM), which directly interacts with the native operating system. The configuration layer also handles interactions between the profile and the JVM.
• The second layer is the profile layer, which consists of the minimum set of application programming interfaces (APIs) for the small computing device.
• The third layer is the Mobile Information Device Profile (MIDP). The MIDP layer contains Java APIs for user network connections, persistence storage, and the user interface. It also has access to CLDC libraries and MIDP libraries.

Here is a presentation that explains the various layers of J2ME Architecture.

Two Components of Small Computing Devices:

A small computing device has two components supplied by the original equipment manufacturer (OEM). These are classes and applications.

• OEM classes are used by the MIDP to access device-specific features such as sending and receiving messages and accessing device-specific persistent data.
• OEM applications are programs provided by the OEM, such as an address book. OEM applications can be accessed by the MIDP.