How Do Ellipses (...) Function in Java Method Signatures (e.g., Varargs)?

Understanding the Ellipsis in Java Method Signatures

Varargs, also called variable-arity methods, are a powerful feature in Java that allow methods to accept a variable number of arguments. They are denoted by an ellipsis (...) at the end of the argument list.

The Ellipsis in withRecipientJids Method

The withRecipientJids method in the App Engine docs has an ellipsis in its signature:

public MessageBuilder withRecipientJids(JID... recipientJids)

This indicates that the method can take any number of JID objects as arguments.

Function of the Ellipsis

When you invoke a varargs method, the arguments passed to the method are transformed into an array of the appropriate type. In this case, the recipientJids parameters will be converted into a JID array.

This allows you to pass multiple arguments to the method without explicitly specifying the exact number. For example, you could call the withRecipientJids method with the following arguments:

msgBuilder.withRecipientJids(jid1, jid2);

This would create a MessageBuilder object with a JID array containing the JIDs jid1 and jid2.

You can also pass a variable number of arguments:

msgBuilder.withRecipientJids(jid1, jid2, jid78_a, someOtherJid);

In this case, the JID array would contain the JIDs jid1, jid2, jid78_a, and someOtherJid.

Varargs provide flexibility and allow methods to be more concise and easier to use.

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