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

Today, I will talk to you about how to understand the J2ME architecture, which may not be well understood by many people. in order to make you understand better, the editor has summarized the following. I hope you can get something from this article.

Do you know anything about J2ME architecture? here I would like to share with you that J2ME is mainly used on small embedded devices. Compared with ordinary PC devices, these devices have no unified hardware standard and operation mode, and their functions are very different.

Introduction to 1.J2ME

J2ME is a highly optimized Java runtime environment that widely targets consumer information products. Most of these classes retain the classes of J2SE and J2EE, but are optimized and updated according to the mobile device. J2ME is mainly used on small embedded devices. Compared with ordinary PC devices, these devices have no unified hardware standard and operation mode, and their functions are very different.

2.J2ME architecture

At present, a lot of data divide the system of J2ME into three. Namely: JVM, configuration and profile. Some materials are also divided into four parts, and some optional packages or API are added in the middle of the configuration and summary table. Let's make a simple explanation for the four-tier architecture: if we add one more layer, it is the OS layer. JVM, configuration and profile form the J2ME running environment. The detailed explanations and functions for each level are as follows:

1) JVM.

JVM in 2 is provided in J2ME. Because JVM is necessary for java code to run, only JVM on any device can well explain the key technology of "compile once, run everywhere". Then JVM is also needed as the interface between the operating system and java applications in embedded or mobile devices. However, due to the limitation of memory, the JVM of embedded devices should also be provided specially. The JVM provided in J2ME is divided into CVM and KVM, which is a scaled-down version of JVM, and KVM is slightly weaker than CVM. CVMCompactVirtualMachine, at first, was interpreted in this way, but then it didn't make any sense to C. But the CVM virtual machine mainly runs on embedded devices with large storage capacity, such as videophone. POS cash register and so on. KVM is part of the smallest runtime environment, that is, for CPU and devices with less memory, where K means kilobytes. KVM is mainly used for small devices such as mobile phones and personal digital assistants (PAD).

2) introduction to J2ME configuration

There are two types of J2ME configurations currently available, CDC and CLDC. CDC (ConnectionDeviceConfiguration) connection device configuration is mainly used for devices with large storage capacity and memory 2MB or above, mostly using CVM virtual machines. It has many user interfaces. The network bandwidth is limited, so there are many different summary tables. And its characteristic is to support floating-point numbers. Contains all the classes and interfaces defined in CLDC. CLDC (ConnectionLimitedDeviceConfiguration) Limited connection device configuration. It is mainly used in small devices with small resources, for embedded systems with less memory than 512Kb. The KVM virtual machine is adopted. Its characteristic is that many J2SE classes and interfaces are not implemented, and the characteristic is that floating point numbers are not supported. For example, the bank's POS machine, which supports floating-point numbers and has a large memory, must be a CDC-like device. On the other hand, because of the small memory of personal mobile phones, floating point numbers are definitely not supported. Using the KVM virtual machine.

3) MIDP (MobileInformationDeviceProfile) Mobile Information device Summary

This is mainly aimed at CLDC devices. It includes three life cycles and event handling mechanisms. Paused state: the program is in a paused state, method: pauseApp (); Actived state: the program is in a running active state. Method startApp () Destroy status: the state before the end of destruction when the program runs. DestroyApp (); MIDP contains other event handling states and mechanisms.

After reading the above, do you have any further understanding of how to understand the J2ME architecture? If you want to know more knowledge or related content, please follow the industry information channel, thank you for your support.

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