The Java Virtual Machine does not require any particular internal structure for objects. In Sun's current implementation of the Java Virtual Machine, a reference to a class instance is a pointer to a handle that is itself a pair of pointers: one to a table containing the methods of the object and a pointer to the Class object that represents the type of the object, and the other to the memory allocated from the Java heap for the object data.
In some of Sun's implementations of the Java virtual machine, a reference to a class instance is a pointer to a handle that is itself a pair of pointers: one to a table containing the methods of the object and a pointer to the Class
object that represents the type of the object, and the other to the memory allocated from the heap for the object data.
参考:http://docs.oracle.com/javase/specs/jvms/se5.0/html/Overview.doc.html#31069