Question

In the App Engine docs, what is the ellipsis (JID...) for in this method signature?

public MessageBuilder withRecipientJids(JID... recipientJids)

What’s the function of those three dots?

Answer 1

Those are Java varargs. They let you pass any number of objects of a specific type (in this case they are of type JID).

In your example, the following function calls would be valid:

MessageBuilder msgBuilder; //There should probably be a call to a constructor here ;)
MessageBuilder msgBuilder2;
msgBuilder.withRecipientJids(jid1, jid2);
msgBuilder2.withRecipientJids(jid1, jid2, jid78_a, someOtherJid);

See more here:
http://java.sun.com/j2se/1.5.0/docs/guide/language/varargs.html