Java HotSpot Virtual Machine

A symbolic reference is a character string that gives the name and possibly other information about the referenced item -- enough information to uniquely identify a class, field, or method. Thus, symbolic references to other classes give the full name of the class. Symbolic references to the fields of other classes give the class name, field name, and field descriptor. Symbolic references to the methods of other classes give the class name, method name, and method descriptor.

When a class file is loaded, it contains symbolic references to other classes and their fields and methods. Dynamic linking is the process of resolving symbolic references into direct references. As the JVM executes bytecodes and encounters an opcode that, for the first time, uses a symbolic reference to another class, the virtual machine must resolve the symbolic reference. The virtual machine performs two basic tasks during resolution:
- It finds the class being referenced (loading it if necessary).
- It replaces the symbolic reference with a direct reference, such as a pointer or offset, to the class, field, or method.
The virtual machine remembers the direct reference so that if it encounters the same reference again later, it can immediately use the direct reference without needing to spend time resolving the symbolic reference again.