The section 1.4.6 of the Java to IDL specification (00-01-06) says the following:

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The stub class corresponding to an RMI/IDL interface or implementation class may
either be in the same package as its associated interface or class, or may be further
qualified by the org.omg.stub package prefix. For example, the stub class for an
RMI/IDL interface class a.b.Fred would be named either a.b._Fred_Stub or
org.omg.stub.a.b._Fred_Stub. For an RMI/IDL implementation class
x.y.Z, the tie class would be named x.y._Z_Tie.
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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  A simple example shows (see below), that in case of RI, the name of generated class will be not x.y._Z_Tie, but org.omg.stub.x.y._Z_Tie.

bash-2.03$ cd /java/re/jdk/1.5.0_06/promoted/all/b02/binaries/solaris-sparc
bash-2.03$ bin/rmic -d /home/as157050/tmp/classes -classpath jre/lib/rt.jar -v1.2 -iiop -keepgenerated javax.management.remote.rmi.RMIServerImpl

bash-2.03$ cd /home/as157050/tmp

  The list of generated files looks like this:

./classes/javax/management/remote/rmi/RMIServerImpl_Stub.java
./classes/javax/management/remote/rmi/RMIServerImpl_Stub.class
./classes/org/omg/stub/javax/management/remote/rmi/_RMIServerImpl_Tie.java
                                                   ^^^^^^^^^^^^^^^^^^^^^^^
./classes/org/omg/stub/javax/management/remote/rmi/_RMIServer_Stub.java
./classes/org/omg/stub/javax/management/remote/rmi/_RMIConnection_Stub.java
./classes/org/omg/stub/javax/management/remote/rmi/_RMIServerImpl_Tie.class
                                                   ^^^^^^^^^^^^^^^^^^^^^^^^
./classes/org/omg/stub/javax/management/remote/rmi/_RMIServer_Stub.class
./classes/org/omg/stub/javax/management/remote/rmi/_RMIConnection_Stub.class