<P> One of Oracle's JVMs is named HotSpot, the other, inherited from BEA Systems is JRockit . Clean - room Java implementations include Kaffe, IBM J9 and Skelmir's CEE - J. Oracle owns the Java trademark and may allow its use to certify implementation suites as fully compatible with Oracle's specification . </P> <P> One of the organizational units of JVM byte code is a class . A class loader implementation must be able to recognize and load anything that conforms to the Java class file format . Any implementation is free to recognize other binary forms besides class files, but it must recognize class files . </P> <P> The class loader performs three basic activities in this strict order: </P> <Ol> <Li> Loading: finds and imports the binary data for a type </Li> <Li> Linking: performs verification, preparation, and (optionally) resolution <Ul> <Li> Verification: ensures the correctness of the imported type </Li> <Li> Preparation: allocates memory for class variables and initializing the memory to default values </Li> <Li> Resolution: transforms symbolic references from the type into direct references . </Li> </Ul> </Li> <Li> Initialization: invokes Java code that initializes class variables to their proper starting values . </Li> </Ol>

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