Introduce several important concepts of J2's

The J2EE platform has several important concepts, such as memory, CLDC, and MIDP. Beginners usually do not have a deep understanding of these concepts, and even have deviations. The purpose of this article is to describe the important concepts related to J2's.
1. Memory
We have been emphasizing that the memory size of mobile information devices is very small and should be cherished. However, we seldom know how these memories are classified. The following is a detailed introduction. In fact, the Memory of the MIDP device is divided into three types: Programme Memory, Heap, and persistent Storage.
Programme Memory is the space allocated by mobile information devices to the MIDlet suite. Because the MIDlet suite is published in a jar file, the size of this file can be considered as the size of Programme Memory. Some vendors have limits on the maximum value of Programme Memory. For example, if the maximum value of my Nokia 6108 is 64 k, the installation will not be available if the maximum value is exceeded. It is very important to reduce the size of the MIDlet suite. A convenient method is to use the obfuscator to confuse the application, which can reduce the size of the jar file. In future articles, I will talk about how to use Proguard.
Heap is the storage space of the objects created during the application running. Local variables and member variables are also stored on Heap, the Heap space provided by the MIDP device is about several dozen k to several hundred K.
The Persistent Storage space is used to implement the local data Persistent Storage of the MIDP Application. I will not talk about the Record Management System in detail from entry to entry.
2. Connected Limited Device Configuration
CLDC includes a Java virtual machine and a series of basic classes. The expert group of j2s' has abstracted the hardware of mobile information devices to obtain their features, and then designed and implemented a Java virtual machine running on mobile information devices, we usually call it KVM. CLDC1.0 also provides a base class consisting of java. io, java. lang, javax. microediton. io, and java. util. Java. lang. ref is added to CLDC1.1.
3. Mobile Infomation Device Profile
MIDP runs on the basis of CLDC. In MIDP, it defines a subset of the application life cycle, user graphical interface, and data management system, thus building the j2_based platform. Generally, the j2-based platform consists of one CLDC and one or more profiles.