Author: Move2008 Source: Move2008.com the third talk in detail J2ME J2ME configuration can be configured in several different configurations. Just as previously mentioned, each configured to provide the smallest Java platform for a set of generic devices, so far, there are only two configuration specifications. Both configurations defined by the Java specification are Connected Limited Device Configuration (Connection Device Configuration, CLDC), and Connected Device Configuration. CLDC is designed to use smaller storage capacity (see Figure 3). CLDC is used to store consumer electronic devices between 128 and 512K, and typically represent devices in this category contains tongs, mobile phones, PDAs and POS terminals; and on the other hand, CDC is used to small but ratio than PC but ratio 512K memory is more equipment, including internet network TV systems, set-top boxes, POS systems, car navigation, and entertainment systems. In general, the CDC makes the small device as long as a small amount of resources, at least more than a resource that is less than the desktop, and CLDC makes the resources owned by the small device, as long as a smart card, Java can be programmed. . Figure 2 Interpretation of the range J2ME has two configurations of CLDC and CDC, CLDC is designed to use smaller storage capacity, while CDC is used to small than the PC but have more than 512K memory. In addition to the necessary conditions for virtual machines in capacity and capabilities, the configuration also specifies that the class application interface should include common java.io, java.net, java.util and java.lang package, and the configuration may include other The package you need. CLDC CLDC The origin can be traced back to Sun's first pocket Java and the first KVM and related class libraries, although CLDC and all configurations meet the conditions of virtual machines, but it itself Not a virtual machine, the reference to the CLDC is only included in the current distribution of KVM. According to the specification, the device running CLDC should have 512K or less memory space, a limited power supply (usually using battery), limited or intermittent network connectivity (9600 BPS or less) and diversity The user interface does not even have a user interface. In general, this configuration is designed for personalized, mobile, limited connection information devices such as both a call, mobile phone, and PDA. Compared to J2SE, CLDC lacks the following characteristics: AWT (Abstract Window Development Cap), Swing or other graphics library user defined the ultimately improved reference RMI Reflection (mapping) CLDC has four packages : Java.lang, java.util, java.io and javax.microEdition. In addition to the microEdition package, the other these packages are the core subset of J2SE packages, and CLDC uses these J2SE libraries, but some of them are not used in micro devices, attributes, attributes, and methods. Therefore, the CLDC class library has many subtle differences. If you want to study the difference between the J2SE and CLDC class libraries, see related documents, which will not be described in detail here. Want to understand why CLDC removes the important classes and features in J2SE, please recall the two basic principles related to CLDC. First, it only has 512K memory space, and the memory like RMI and mapping is too large. Second, the configuration must meet the minimum Java platform for a set of universal devices. In the field of personal mobile information equipment, many systems cannot support many advanced features in J2SE.
