Learning UML 2.0 by Russ Miles & Kim Hamilton

Author:Russ Miles & Kim Hamilton [Russ Miles]
Language: eng
Format: epub
Tags: COMPUTERS / Software Development & Engineering / General
ISBN: 9780596159450
Publisher: O'Reilly Media
Published: 2008-12-16T16:00:00+00:00

Asynchronous Messages

It would be great if all the interactions in your system happened one after the other in a nice simple order. Each participant would pass a message to another participant and then calmly wait for the message to return before carrying on. Unfortunately, that's not how most systems work. Interactions can happen at the same point in time, and sometimes you will want to initiate a collection of interactions all at the same time and not wait for them to return at all.

For example, say you are designing a piece of software with a user interface that supports the editing and printing of a set of documents. Your application offers a button for the user to print a document. Printing could take some time, so you want to show that after the print button is pressed and the document is printing, the user can go ahead and work with other things in the application. The regular synchronous message arrow is not sufficient to show these types of interactions. You need a new type of message arrow: the asynchronous message arrow.

An asynchronous message is invoked by a Message Caller on a Message Receiver, but the Message Caller does not wait for the message invocation to return before carrying on with the rest of the interaction's steps. This means that the Message Caller will invoke a message on the Message Receiver and the Message Caller will be busy invoking further messages before the original message returns, as shown in Figure 7-10.

A common way of implementing asynchronous messaging in Java is to use threads, as shown in Example 7-2.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.