These are mainly used when some objects are added to a consumer and the consumer will reference the object weakly. In this case the consumer returns a token which should be kept until the client is done with the consumer.
When the token is no longer referenced, the added object to the consumer might be freely garbage collected, and therefore automatically uninstalling the object from the consumer.
This is mainly useful when event listeners are installed over an RMI connection. It can cause a memory leak if the consumer strongly references the listener, as abruptly terminating the RMI connection will leave the listener installed. By weakly referencing, and returning a token, when the token is no longer referenced, the consumer can automatically uninstall the listener when it is garbage collected.
Note that in most cases explicitly uninstalling the object from the consumer is beneficial rather than
nulling out the references to the token.
Tokens should strongly reference the subject of the operation.