A client uses the runtime infrastructure to locate and contact desired services. Once the services have been contacted, the client can use the programming model to enlist the help of the services in achieving the client's goals. Lookup services are the central organizing mechanism for Jini technology-based systems. When devices are plugged into the network, they register themselves with a lookup service and become part of a federation. When clients wish to locate a service to assist with some task, they consult a lookup service.
Lookup services organize the services they contain into groups.
A group is simply a set of registered services identified by a string. This kind of redundancy can help make the Jini technology system more fault tolerant. The runtime infrastructure enables services to register with lookup services through a process called discovery and join . Discovery is the process by which a Jini technology-enabled device locates lookup services on the network and obtains references to them. Join is the process by which a device registers the services it offers with lookup services.