Resolve the three important concepts

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 in j2's. See the following for details.

Several important concepts

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 describes the memory in the J2EE platform in detail. In fact, the memory of the MIDP device is divided into three types: ProgrammeMemory, Heap, and persistentStorage.

ProgrammeMemory is the space allocated by mobile information devices to the MIDletsuite. Because the MIDletsuite is released in a jar file, the size of this file can be considered as the size of ProgrammeMemory. Some vendors have limits on the maximum value of ProgrammeMemory. For example, if the maximum value of my Nokia6108 is 64 k, installation cannot be performed if the maximum value is exceeded. It is very important to reduce the size of the MIDletsuite. 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 PersistentStorage space is used to implement the local data persistent storage of the MIDP application. I have made a detailed introduction to the RecordManagementSystem from the beginning to the mastery.

2. ConnectedLimitedDeviceConfiguration

The cldc in the j2m‑based platform includes a Java virtual machine and a series of basic classes. The Expert Group of the j2-based platform abstracts the hardware of mobile information devices to obtain their features, then we design and implement 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. MobileInfomationDeviceProfile

The MIDP Platform runs on CLDC. In the MIDP, it defines a subset of the application life cycle, user graphical interface, and data management system, and thus builds the j2e-based platform. Generally, the j2-based platform consists of one CLDC and one or more profiles.