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copied!<p>The Streams in Java - subclasses of <code>InputStream</code> and <code>OutputStream</code> are perfect examples of the decorator pattern.</p> <p>As an example, writing a file to disk:</p> <pre><code>File toWriteTo = new File("C:\\temp\\tempFile.txt"); OutputStream outputStream = new FileOutputStream(toWriteTo); outputStream.write("Sample text".getBytes()); </code></pre> <p>Then should you require some extra functionality regarding the writing to disk:</p> <pre><code>File toWriteTo = new File("C:\\temp\\tempFile.txt"); OutputStream outputStream = new GZIPOutputStream(new FileOutputStream(toWriteTo)); outputStream.write("Sample text".getBytes()); </code></pre> <p>By simply "chaining" the constructors, you can create quite powerful ways of writing to disk. The beauty in this way is that you can add different (in this example) <code>OutputStream</code> implementations later on. Also, each implementation doesn't know how the others work - they all just work to the same contract. This also makes testing each implementation very easy in isolation.</p> <p><hr> There are plenty of "real world" examples of where the decorator pattern can be used. Off the top of my head, some examples:</p> <ul> <li>Reading and writing to disk (above)</li> <li>Construction of UI elements, such as adding scrollbars on to text areas etc</li> </ul> <p>Head First Design Patterns has some more "real world" examples. It seems that O'Reilly has their sample chapter, which is on Decorator Pattern, for free; Google showed up this link: <strong><a href="http://oreilly.com/catalog/hfdesignpat/chapter/ch03.pdf" rel="noreferrer">PDF</a></strong> </p>

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