Research And Practice Of JAVA Virtual Machine Technology

JAVA architecture includes four relative technologies,namely JAVA Language, JAVA API, Class File and JAVA Virtual Machine (JVM). The JAVA Virtual Machine is the key part of the JAVA technologies. As the same as an actual computer, JVM is an abstract computer, which has its own instruction set and uses different memory area. By giving an insight into the JVM, we can fast master the advanced computer technology , and get a vast amount of experience. Then we can apply these technologies to our national software development and design, and make a contribution to our national software development.The JVM adopts stack structure. In this paper, we firstly study the architecture of the JAVA Virtual Machine, including Class Loader, Runtime Data Area and Garbage collection. Garbage collection is also an attractive feature of JAVA language. In this paper, we research the classical garbage collection technologies and some advanced algorithms, and focus on the train algorithm. With the deeply researching on the train algorithm, we find that the train algorithm has the following problems: (1) the process is not explicitly presented when the object is transferred by several trains; (2) it is still destructive when deals with the popular object; (3) it is subtle in some special conditions. In the paper, we give our theoretical solution and process scheme for these three problems.We mainly research the Class Loader system. Firstly we analyze the structure of the Class Loader, such as parent-child accreditation mode, the format of class file and so on. In this paper, we design and implement a class loader, which main function is as followings: find class file according to the setup of system environment variable, check the validity of class file, parse class file and then create corresponding memory method data structure. In addition, it is found that all present class loaders can not load the encrypted file. In this paper, we propose an improved scheme, and design an encrypt algorithm which is used to encrypt the class file. The improved class loader firstly calls the corresponding decrypt algorithm to reduce original class file, then validates and loads this data.