Shulou(Shulou.com)06/02 Report--

In this issue, the editor will bring you about how to trace the origin and development of Java ME technology. The article is rich in content and analyzes and narrates it from a professional point of view. I hope you can get something after reading this article.

To describe Java ME technology, Java ME used to be called J2ME _ Java2MicroEdition (J2ME) is a part of Java2, which is also called J2SE and J2EE. According to the definition of Sun: J2ME is a highly optimized Java operating environment, mainly for consumer electronic devices, such as cellular phone and videophone, digital set-top box, car navigation system and so on.

Java ME concept

J2ME (Java2MicroEdition) is a part of Java2, which is called together with J2SE and J2EE. According to the definition of Sun: J2ME is a highly optimized Java operating environment, mainly for consumer electronic devices, such as cellular phone and videophone, digital set-top box, car navigation system and so on. J2ME technology was officially launched at the JavaOneDeveloperConference conference in 1999. It transplants the platform-independent features of Java language to small electronic devices and allows mobile wireless devices to share applications.

Design specification

When designing its specifications, J2ME follows the basic principle that it is meaningless to create a single development system for a variety of different devices. So J2ME first divides all embedded devices into two categories: one is embedded devices with limited computing functions and limited power supply (such as PDA and mobile phones); the other is embedded devices with relatively good computing power and relatively sufficient power supply (such as air conditioners, refrigerators, TV set-top boxes (set-topbox)). Because of these two types of embedded devices, Java introduces a concept called Configuration, and then defines the above-mentioned embedded devices with limited computing function and limited power in the ConnectedLimitedDeviceConfiguration (CLDC) specification, while the other device is specified as the ConnectedDeviceConfiguration (CDC) specification. In other words, J2ME first divides all embedded devices into two abstract types using the concept of Configuration.

In fact, here we can think of Configuration as the specification of J2ME for two types of embedded devices, and these specifications define at least the computing power, power supply capacity, memory size and other specifications that these devices should comply with. At the same time, a set of class function libraries that can be used by Java programs executed on these devices are defined as subsets of Java standard core class function libraries and extended class function libraries consistent with the characteristics of this type of device. For example, in the CLDC specification, the core class libraries that can be supported are java.lang.*, javaio.*, and java.util.*, while the extended class libraries supported are javamicroeditionio.*. After distinguishing between the two main Configuration, J2ME then defines the concept of Profile. Profile is a specification based on Configuration. The reason why there is the concept of Profile is to distinguish more clearly how Java programs on various embedded devices should be developed and what functions they should have. Therefore, the extended class library which is very related to specific embedded devices is defined in Profile, and how to present the user interface of Java programs on various embedded devices is defined in Profile. The extended class library defined in Profile is based on the core class library defined in the underlying Configuration.

Architecture introduction

Compared with J2SE and J2EE

Compared with J2SE and J2EE, Java ME has a more diverse operating environment and goals, but each product has a more single use and more stringent resource constraints. In order to achieve standardization and compatibility while trying to meet different requirements, the architecture of J2ME is divided into Configuration, Profile and OptionalPackages (optional package). The combination of them forms a specific operating environment.

Configuration is mainly a vertical classification of devices, which includes storage and processing capabilities, in which virtual machine characteristics and basic class libraries are defined. Configuration that has been standardized are-ConnectedLimitedDeviceConfiguration (CLDC) and ConnectedDeviceConfiguration (CDC).

Foundation establishment

Profile is built on the basis of Configuration and constitutes a complete running environment. It classifies the equipment horizontally, segmenting the market for specific areas, and mainly includes specific purpose class libraries and API. The standardized Profile on CLDC is MobileInformationDeviceProfile (MIDP) and InformationModuleProfile (IMP), while the standardized Profile on CDC is FoundationProfile (FP), PersonalBasisProfile (PBP) and PersonalProfile (PP).

Optional packages provide additional, modular, and more diverse features independent of the previous two. Currently standardized optional packages include database access, multimedia, Bluetooth, and so on.

Development tools

The development of Java ME programs generally do not need special development tools, developers only need to install JavaSDK and download free SunJavaWirelessToolkit to start writing Java ME programs, compilation and testing, in addition, the major IDE (Eclipse and NetBeans) support Java ME development, individual mobile phone developers such as Nokia and SonyEricsson have their own SDK for developers to develop programs compatible with their platform.

The above is the editor for you to share how to trace the origin and development of Java ME technology, if you happen to have similar doubts, you might as well refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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