Exercise 21-1. Modify the remote banking example in this chapter so that bank
customers are allowed to borrow money from the bank against some
maximum line of credit, and so they can also apply money from their
account to pay off their debt. Add borrow( ) and
repay( ) methods to the
RemoteBank interface, implement these methods with
RemoteBankServer or
PersistentBankServer, and modify the client so
that it can call these methods when the user requests them.
Exercise 21-2. The rmiregistry program provides a simple name
service for RMI programs; it allows servers to register names for the
remote objects they serve, and it allows clients to look up those
remote objects by name. Because it is a global registry, shared by
any number of remote services, there is a possibility of name
collisions. For this reason, if a service needs to define names for a
number of remote objects, it should usually provide its own custom
registry. That way, a client can use the global registry to look up
the service's custom naming registry, and then it
can use this custom registry to look up particular named objects for
that service.
Use RMI to write a server that provides such a custom naming service.
It should export remote methods that correspond to the bind(
), rebind( ), unbind(
), and lookup( ) methods of the
Naming class. You will probably want to use a
java.util.Map object to associate names with
remote objects.
Exercise 21-3. The MUD example of this chapter uses remote objects to represent the
rooms or places in the MUD and the people interacting in the MUD.
Things that appear in the MUD, however, are not remote objects; they
are simply part of the state of each room in the MUD.
Modify the example so that things are true remote objects. Define a
MudThing interface that extends
Remote. It should have a getDescription(
) method that returns the description of a thing. Modify
the MudPlace interface and
RemoteMudPlace class to have methods that allow
MudThing objects to be added to and removed from a
place.
Define a trivial implementation of MudThing that
simply returns a static string from its getDescription(
) method. Then, define another implementation of
MudThing, named Clock. This
class should have more dynamic behavior: whenever its
getDescription( ) method is called, it should
return a string that displays the current time. Modify the MUD server
so that it places a Clock object in the entrance
to the MUD.
Exercise 21-4. Modify the MUD example again so that MudPerson
objects can pick up MudThing objects they find in
a MudPlace, carry them around, drop them in other
places, and give them to other people. Implement at least three new
methods: pickup( ), drop( ),
and give( ). Modify the MUD client so that it
supports pickup, drop, and give commands.
