J2ME Development Getting Started Series: J2ME Overview
Keywords: Java; J2ME source: air network
We will start from the definition J2ME, from the simplest J2ME to start. Then discuss its overall architecture and learn J2ME target equipment. As part of the architecture discussion, we will provide an overview of briefs and configurations. At the same time, we will briefly introduce some precautions in the Package and configure the J2ME application process. What is J2ME? Sun Microsystems defines J2ME as "a highly optimized Java runtime environment with a wide range of consumer products, including pagers, mobile phones, visual calls, digital set-top boxes and car navigation systems." Since 1999 6loper Conference After the declaration, J2ME brings a cross-platform function of the Java language to a small device, allowing mobile wireless devices to share applications. With J2ME, Sun has enabled the Java platform to adapt to the integrated or small computing device monthly products in Javaone DEVE. J2ME Overall Architecture J2ME uses configuration and briefing to customize Java runtime environment (JRE). As a complete JRE, J2Me consists of configuration and profile, the configuration determines the JVM used, and the brief table defines the application by adding a domain class. Configuration Define the Basic Runtime Environment as a set of core classes and a specific JVM running on a particular type of device. We will discuss the configuration in the J2ME configuration chapter. A brief mesh definition application; specifically, it adds a certain field-specific class to the J2ME configuration to define a role of the device. We will introduce a brief watch in the J2ME Summary. The following chart describes the relationship between different virtual machines, configuration, and briefs. It compares the J2SE API and its Java virtual machine. Although J2SE virtual machines are often referred to as a JVM, J2ME virtual machines, KVM and CVM are JVM subsets. KVM and CVM can be seen as a Java virtual machine - they are the compressed version of J2SE JVM and J2ME.
Configuration overview
Configuration Define the Basic Runtime Environment as a set of core classes and a specific JVM running on a particular type of device. Although other configurations may be defined in the future, there are two configurations of the current J2ME:
1. Connection Restriction Device Configuration (CLDC) is specifically used with KVM for 16-bit or 32-bit devices for memory. This is a configuration (virtual machine) for developing a small J2ME application. (From the developer's perspective) Its size limit makes it more interesting than CDC, more challenging. CLDC is also a configuration for developing a drawing tool application. The Palm computer is an example of a small wireless device running a small application. We will introduce CLDC in subsequent article in this split.
2. Connection Equipment Configuration (CDC) is used with C Virtual Machine (CVM) to require memory more than 2 megabyte architectures. Internet TV set-top box is an example of such devices. Although we will briefly introduce CDC in chapter of the CDC API, it is not within the scope of this tutorial.
Summary outline
The brief mesh defines the type of device supported by your application. In particular, it adds to the J2ME configuration to a domain class to define a role of the device. The brief table is built on the top of the configuration. Two briefings have been defined for J2ME: KJAVA and Move Information Device Summary (MIDP), which are also built on CDLC. These two briefings are suitable for small devices.
There is an outline, you can create your own brief table above it, which is also known as a basic table, which is available for CDC. However, in this tutorial, we only focus on the top of the CLDC and apply to a small device. We will discuss these briefings in later articles and use Kjava and MIDP to build some sample applications.
J2ME target equipment
Target devices for J2ME applications developed using CLDC typically have the following features: 160 to 512 kilobytes of 160 to 512 kilobytes available for Java platforms.
Limited power, often battery power
Network connectivity, often wireless, inconsistent connection and limited bandwidth
The user interface is confusing, the degree is uneven; sometimes there is no interface at all
Some CLDC supported equipment, including wireless phones, pager, mainstream personal digital assistant (PDA), and small retail payment terminals.
The target devices of the CDC usually have the following characteristics in accordance with Sun Microsystems.
Use 32-bit processor
2 megabytes or more total memory available for Java platform
All functions of the Java 2 "Blue Paper" virtual machine required by the equipment
Network connectivity, often wireless, inconsistent connection and limited bandwidth
The user interface is confusing, the degree is uneven; sometimes there is no interface at all
Some CDC supported equipment, including resident gateways, smart phones, and communications, PDAs, manager, household appliances, sales network terminals, and car navigation systems.
Comparison between J2ME, J2SE and J2EE
The following chart describes the device that supports J2ME applications, and the J2ME is suitable for the Java platform:
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