Demystifying the Ellipsis in Method Signatures

Question:

Within the App Engine documentation, the withRecipientJids method signature includes an ellipsis (JID...). What purpose does this three-dot notation serve?

Answer:

Those three dots represent Java varargs (variable-length arguments). Varargs allow you to pass any number of objects of a specific type as method arguments.

In the withRecipientJids method, the varargs allow you to provide a variable number of JID objects as recipients. This means you can use the method to send mensagens to multiple recipients with varying lengths.

For example, the following function calls are both valid:

MessageBuilder msgBuilder = new MessageBuilder();
msgBuilder.withRecipientJids(jid1, jid2);

MessageBuilder msgBuilder2 = new MessageBuilder();
msgBuilder2.withRecipientJids(jid1, jid2, jid78_a, someOtherJid);

In the first call, the method takes two recipients. In the second call, it takes four recipients. The varargs allow the method to accept any number of JID objects as arguments.

Varargs Syntax:

Varargs are denoted by the three-dot notation after the argument type, as seen in:

public void myMethod(int... numbers)

This signature indicates that the myMethod method can take any number of int arguments.

Further Resources:

For a more detailed explanation of Java varargs, refer to the official documentation:

• [Java Varargs](https://docs.oracle.com/javase/tutorial/java/javaOO/arguments.html#variable)