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/website/features/experimental/Wither.html

http://github.com/rzwitserloot/lombok
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  1. <!DOCTYPE html>
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  2. <html><head>
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  7. 	<meta name="description" content="Spice up your java" />
    8. 

  8. 	<title>EXPERIMENTAL – @Wither</title>
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  9. </head><body><div id="pepper">
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  10. 	<div class="minimumHeight"></div>
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  11. 	<div class="meat">
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  12. 		<div class="header"><a href="../../index.html">Project Lombok</a></div>
    13. 

  13. 		<h1>@Wither</h1>
    14. 

  14. 		<div class="byline">Immutable 'setters' - methods that create a clone but with one changed field.</div>
    15. 

  15. 		<div class="since">
    16. 

  16. 			<h3>Since</h3>
    17. 

  17. 			<p>
    18. 

  18. 				@Wither was introduced as experimental feature in lombok v0.11.4.
    19. 

  19. 			</p>
    20. 

  20. 		</div>
    21. 

  21. 		<div class="experimental">
    22. 

  22. 			<h3>Experimental</h3>
    23. 

  23. 			<p>
    24. 

  24. 			Experimental because:
    25. 

  25. 			<ul>
    26. 

  26. 				<li>Still not sure that <code>@Wither</code> is an appropriate name for this feature.</li>
    27. 

  27. 				<li>Should there be an option to supply a way of cloning the input somehow?</li>
    28. 

  28. 				<li>Should the way that the clone is created by configurable?</li>
    29. 

  29. 				<li>Should we replace @Wither entirely with a builder class?</li>
    30. 

  30. 			</ul>
    31. 

  31. 			Current status: <em>neutral</em> - More feedback requires on the items in the above list before promotion to the main package is warranted.
    32. 

  32. 		</div>
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  33. 		<div class="overview">
    34. 

  34. 			<h3>Overview</h3>
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  35. 			<p>
    36. 

  36. 				The next best alternative to a setter for an immutable property is to construct a clone of the object, but with a new value for this one field.
    37. 

  37. 				A method to generate this clone is precisely what <code>@Wither</code> generates: a <code>withFieldName(newValue)</code> method which produces a clone
    38. 

  38. 				except for the new value for the associated field.
    39. 

  39. 			</p><p>
    40. 

  40. 				For example, if you create <code>public class Point { private final int x, y; }</code>, setters make no sense because the fields
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  41. 				are final. <code>@Wither</code> can generate a <code>withX(int newXValue)</code> method for you which will return a new point with the supplied
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  42. 				value for <code>x</code> and the same value for <code>y</code>.
    43. 

  43. 			</p><p>
    44. 

  44. 				Like <a href="../GetterSetter.html"><code>@Setter</code></a>, you can specify an access level in case you want the generated wither to be something other than <code>public</code>:<br />
    45. 

  45. 				<code>@Wither(level = AccessLevel.PROTECTED)</code>. Also like <a href="../GetterSetter.html"><code>@Setter</code></a>, you can also put a <code>@Wither</code> annotation on a type, which means
    46. 

  46. 				a 'wither' is generated for each field (even non-final fields).
    47. 

  47. 			</p><p>
    48. 

  48. 				To put annotations on the generated method, you can use <code>onMethod=@__({@AnnotationsHere})</code>; to put annotations on the only parameter of a generated wither method, you can use <code>onParam=@__({@AnnotationsHere})</code>. Be careful though! This is an experimental feature. For more details see the documentation on the <a href="onX.html">onX</a> feature.
    49. 

  49. 			</p><p>
    50. 

  50. 				<em>NEW in lombok v1.12.0:</em> javadoc on the field will now be copied to generated withers. Normally, all text is copied, and <code>@param</code> is <em>moved</em> to the wither, whilst <code>@return</code> lines are stripped from the wither's javadoc. Moved means: Deleted from the field's javadoc. It is also possible to define unique text for the wither's javadoc. To do that, you create a 'section' named <code>WITHER</code>. A section is a line in your javadoc containing 2 or more dashes, then the text 'WITHER', followed by 2 or more dashes, and nothing else on the line. If you use sections, <code>@return</code> and <code>@param</code> stripping / copying for that section is no longer done (move the <code>@param</code> line into the section).
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  51. 			</p>
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  52. 		</div>
    53. 

  53. 		<div class="snippets">
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  54. 			<div class="pre">
    55. 

  55. 				<h3>With Lombok</h3>
    56. 

  56. 				<div class="snippet">@HTML_PRE@</div>
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  57. 			</div>
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  58. 			<div class="sep"></div>
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  59. 			<div class="post">
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  60. 				<h3>Vanilla Java</h3>
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  61. 				<div class="snippet">@HTML_POST@</div>
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  62. 			</div>
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  63. 		</div>
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  64. 		<div style="clear: left;"></div>
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  65. 		<div class="overview confKeys">
    66. 

  66. 			<h3>Supported configuration keys:</h3>
    67. 

  67. 			<dl>
    68. 

  68. 			<dt><code>lombok.wither.flagUsage</code> = [<code>warning</code> | <code>error</code>] (default: not set)</dt>
    69. 

  69. 			<dd>Lombok will flag any usage of <code>@Wither</code> as a warning or error if configured.</dd>
    70. 

  70. 			</dl>
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  71. 		</div>
    72. 

  72. 		<div class="overview">
    73. 

  73. 			<h3>Small print</h3><div class="smallprint">
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  74. 				<p>
    75. 

  75. 					Withers cannot be generated for static fields because that makes no sense.
    76. 

  76. 				</p><p>
    77. 

  77. 					Withers can be generated for abstract classes, but this generates an abstract method with the appropriate signature.
    78. 

  78. 				</p><p>
    79. 

  79. 					When applying <code>@Wither</code> to a type, static fields and fields whose name start with a $ are skipped.
    80. 

  80. 				</p><p>
    81. 

  81. 					For generating the method names, the first character of the field, if it is a lowercase character, is title-cased, otherwise, it is left unmodified.
    82. 

  82. 					Then, <code>with</code> is prefixed.
    83. 

  83. 				</p><p>
    84. 

  84. 					No method is generated if any method already exists with the same name (case insensitive) and same parameter count. For example, <code>withX(int x)</code>
    85. 

  85. 					will not be generated if there's already a method <code>withX(String... x)</code> even though it is technically possible to make the method. This caveat
    86. 

  86. 					exists to prevent confusion. If the generation of a method is skipped for this reason, a warning is emitted instead. Varargs count as 0 to N parameters.
    87. 

  87. 				</p><p>
    88. 

  88. 					For <code>boolean</code> fields that start with <code>is</code> immediately followed by a title-case letter, nothing is prefixed to generate the wither name.
    89. 

  89. 				</p><p>
    90. 

  90. 					Any annotations named <code>@NonNull</code> (case insensitive) on the field are interpreted as: This field must not ever hold
    91. 

  91. 					<em>null</em>. Therefore, these annotations result in an explicit null check in the generated wither. Also, these
    92. 

  92. 					annotations (as well as any annotation named <code>@Nullable</code> or <code>@CheckForNull</code>) are copied to wither parameter.
    93. 

  93. 				</p>
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  94. 			</div>
    95. 

  95. 		</div>
    96. 

  96. 		<div class="footer">
    97. 

  97. 			<a href="index.html">Back to experimental features</a> | <a href="Delegate.html">Previous feature (@Delegate)</a> | <a href="onX.html">Next feature (onX)</a><br />
    98. 

  98. 			<a href="../../credits.html" class="creditsLink">credits</a> | <span class="copyright">Copyright &copy; 2009-2016 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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