URIs for new comments and attachments?

I am using JIRA Rest JAVA API, trying to create new comments and add new attachments.
All the methods for adding those thing asking for URIs (see below).
My question is: how to get or construct URLs for new comments/attachments?
For example, I want to attach a PDF file named “myfile.pdf”, then what’s the attachmentsUri I should pass to the method?
Same for new comments: what’s the value of commentsUri?

IssueRestClient.addAttachment(URI attachmentsUri, InputStream in, String filename)
IssueRestClient.addAttachments(URI attachmentsUri, AttachmentInput… attachments)
IssueRestClient.addAttachments(URI attachmentsUri, File… files)
IssueRestClient.addComment(URI commentsUri, Comment comment)

Thanks in advanced!