Using JAVA SDK for Cleanroom

Hello.

Scroll to the "See Also" section on each action's page in the documentation for links to available SDK documentation.
You can open the documentation for each SDK from this link.
https://docs.aws.amazon.com/clean-rooms/latest/apireference/API_ListCollaborations.html#API_ListCollaborations_SeeAlso

Since there is no description, I don't know how to pass some parameters, such as https://docs.aws.amazon.com/clean-rooms/latest/apireference/API_ListCollaborations.html need parm nextToken, How can I get it?

Parameters that are required for API requests are marked "Required: Yes" in the documentation.
"nextToken" does not have "Required: Yes" written in it, so you can request it without setting it.
For example, the option "collaborationIdentifier" of the API "ListCollaborationPrivacyBudgetTemplates" is written as "Required: Yes", so setting is required.
By the way, "nextToken" is included in the response when there are many output results.
https://docs.aws.amazon.com/clean-rooms/latest/apireference/API_ListCollaborationPrivacyBudgetTemplates.html