MacIntosh programmers use the term handle to mean a pointer to a pointer.

Java references are usually implemented as handles.

The advantage of a JVM that implements Java references as pointers (direct machine addresses) is speed.

The advantage of a JVM that implements Java references as handles (pointers to pointers) is ease of shuffling objects around in RAM to reduce memory fragmentation. Handles allow the thing pointed to be moved, and all references are thereby automatically forwarded to the new location. You only need to update one place when the location of the object changes.