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Reinier Zwitserloot
89 lines
6.0 KiB
HTML
89 lines
6.0 KiB
HTML
<!DOCTYPE html>
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<html><head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<link rel="stylesheet" type="text/css" href="../../logi/reset.css" />
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<link rel="stylesheet" type="text/css" href="../features.css" />
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<link rel="shortcut icon" href="../../favicon.ico" type="image/x-icon" />
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<meta name="description" content="Spice up your java" />
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<title>onX</title>
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</head><body><div id="pepper">
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<div class="minimumHeight"></div>
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<div class="meat">
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<div class="header"><a href="../../index.html">Project Lombok</a></div>
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<h1>onX</h1>
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<div class="byline">Sup dawg, we heard you like annotations, so we put annotations in your annotations so you can annotate while you're annotating.</div>
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<div class="since">
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<h3>Since</h3>
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<p>
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onX was introduced as experimental feature in lombok v0.11.8.
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</p>
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</div>
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<div class="experimental">
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<h3>Experimental</h3>
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<p>
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Experimental because:
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<ul>
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<li>Ugly syntax. The syntax of this feature is not optimal, but it is the least convoluted syntax that could possibly work (for now!)</li>
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<li>Possibly java 9 will offer (much) better ways of supporting this feature.</li>
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<li>Uncertainty: Future versions of javac may break this feature, and we may not be able to restore it.</li>
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</ul>
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Current status: <em>uncertain</em> - Currently we feel this feature cannot move out of experimental status.
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</div>
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<div class="overview">
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<h3>Overview</h3>
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<p>
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<strong>This feature is considered 'workaround status' - it exists in order to allow users of lombok that cannot work without this feature to have access to it anyway. If we find a better way to implement this feature, or some future java version introduces an alternative strategy, this feature can disappear without a reasonable deprecation period. Also, this feature may not work in future versions of javac. Use at your own discretion.</strong>
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</p><p>
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Most annotations that make lombok generate methods or constructors can be configured to also make lombok put custom annotations on elements in the generated code.
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</p><p>
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<code>@Getter</code>, <code>@Setter</code>, and <code>@Wither</code> support the <code>onMethod</code> option, which will put the listed annotations on the generated method.
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</p><p>
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<code>@AllArgsConstructor</code>, <code>@NoArgsConstructor</code>, and <code>@RequiredArgsConstructor</code> support the <code>onConstructor</code> option which will put the listed annotations on the generated constructor.
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</p><p>
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<code>@Setter</code> and <code>@Wither</code> support <code>onParam</code> in addition to <code>onMethod</code>; annotations listed will be put on the only parameter that the generated method has. <code>@EqualsAndHashCode</code> also supports <code>onParam</code>; the listed annotation(s) will be placed on the single parameter of the generated <code>equals</code> method, as well as any generated <code>canEqual</code> method.
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</p><p>
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The syntax is a little strange; to use any of the 3 <code>onX</code> features, you must wrap the annotations to be applied to the constructor / method / parameter in <code>@__(@AnnotationGoesHere)</code>. To apply multiple annotations, use <code>@__({@Annotation1, @Annotation2})</code>. The annotations can themselves obviously have parameters as well.
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</p>
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</div>
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<div class="snippets">
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<div class="pre">
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<h3>With Lombok</h3>
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<div class="snippet">@HTML_PRE@</div>
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</div>
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<div class="sep"></div>
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<div class="post">
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<h3>Vanilla Java</h3>
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<div class="snippet">@HTML_POST@</div>
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</div>
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</div>
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<div style="clear: left;"></div>
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<div class="overview">
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<h3>Small print</h3><div class="smallprint">
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<p>
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The reason of the weird syntax is to make this feature work in javac 7 compilers; the <code>@__</code> type is an annotation reference to the annotation type <code>__</code> (double underscore) which doesn't actually exist; this makes javac 7 delay aborting the compilation process due to an error because it is possible an annotation processor will later create the <code>__</code> type. Instead, lombok applies the annotations and removes the references so that the error will never actually occur. The point is: The <code>__</code> type <em>must not exist</em>, otherwise the feature does not work. In the rare case that the <code>__</code> type does exist (and is imported or in the package), you can simply add more underscores. Technically any non-existent type would work, but to maintain consistency and readability and catch erroneous use, lombok considers it an error if the 'wrapper' annotation is anything but a series of underscores.
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</p><p>
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To reiterate: This feature can disappear at any time; if you use this feature, be prepared to adjust your code when we find a nicer way of implementing this feature, or, if a future version of javac forces us to remove this feature entirely with no alternative.
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</p><p>
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The <code>onX</code> parameter is not legal on any type-wide variant. For example, a <code>@Getter</code> annotation on a class does not support <code>onMethod</code>.
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</p>
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</div>
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</div>
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<div class="footer">
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<a href="index.html">Back to experimental features</a> | <a href="Wither.html">Previous feature (@Wither)</a> | <a href="UtilityClass.html">Next feature (@UtilityClass)</a><br />
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<a href="../../credits.html" class="creditsLink">credits</a> | <span class="copyright">Copyright © 2009-2015 The Project Lombok Authors, licensed under the <a href="http://www.opensource.org/licenses/mit-license.php">MIT license</a>.</span>
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