J2ME Overview, Inside and Architecture

J2ME (Java 2 Platform, Micro Edition) is a technology that allows programmers to use the Java programming language and related tools to develop programs.

J2ME OVERVIEW

• The Java development team enhanced the capabilities of Java to dramatically reduce the complexity of developing a multi-tier application.
• The team grouped features of Java into three editions, each having a software development kit (SDK).
• The original edition of Java, called the Java 2 Standard Edition (J2SE), consists of application programming interfaces (APIs) needed to build a Java application or applet.
• The Java 2 Micro Edition (J2ME) contains the API used to create applications for small computing devices, including wireless Java applications.
• The development team at Sun worked on Java in the early 1990s to address the programming needs of the fledgling embedded computer market, but that effort was sidetracked by more compelling opportunities presented by the Internet.
• As those opportunities were addressed, a new breed of portable communications devices opened other opportunities at the turn of the century. Cell phones expanded from voice communications devices to voice and text communications devices.
• Pocket electronic telephone directories evolved into personal digital assistants. Chipmakers were releasing new products at this time that were designed to transfer computing power from a desktop computer into mobile small computers that controlled gas pumps, cable television boxes, and an assortment of other appliances.
• J2ME is a reduced version of the Java API and Java Virtual Machine that is designed to operate within the sparse resources available in the new breed of embedded computers and microcomputers.

Inside J2ME

• Consumers expect the same software and capabilities found on their desktop and laptop computers to be available on their cell phones and personal digital assistants.
• Developers seeking to build applications that run on cell phones, personal digital assistants, and various consumer and industrial appliances must strike a balance between a thick client and a thin client.
• A thick client is front-end software that contains the logic to handle a sizable amount of data processing for the system.
• A thin client is front-end software that depends on back-end software for much of the system processing.
•  Processing on the wireless device might involve two steps: First the software performs a simple validation process to assure that all fields on the form contain information.
• Next the order is transmitted to the back-end system.
• The back-end system 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.
• A key benefit of using J2ME is that J2ME is compatible with all Java-enabled devices. A Java-enabled device is any computer that runs the Java Virtual Machine.

J2ME Architecture

• The modular design of the J2ME architecture enables an application to be scaled based on constraints of a small computing device. 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.
• 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.