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<title>EXPERIMENTAL – @Wither</title>
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<div class="header"><a href="../../index.html">Project Lombok</a></div>
<h1>@Wither</h1>
<div class="byline">Immutable 'setters' - methods that create a clone but with one changed field.</div>
<div class="since">
<h3>Since</h3>
<p>
@Wither was introduced as experimental feature in lombok v0.11.4.
</p>
</div>
<div class="experimental">
<h3>Experimental</h3>
<p>
Experimental because:
<ul>
<li>Still not sure that <code>@Wither</code> is an appropriate name for this feature.</li>
<li>Should there be an option to supply a way of cloning the input somehow?</li>
<li>Should the way that the clone is created by configurable?</li>
<li>Should we replace @Wither entirely with a builder class?</li>
</ul>
Current status: <em>neutral</em> - More feedback requires on the items in the above list before promotion to the main package is warranted.
</div>
<div class="overview">
<h3>Overview</h3>
<p>
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.
A method to generate this clone is precisely what <code>@Wither</code> generates: a <code>withFieldName(newValue)</code> method which produces a clone
except for the new value for the associated field.
</p><p>
For example, if you create <code>public class Point { private final int x, y; }</code>, setters make no sense because the fields
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
value for <code>x</code> and the same value for <code>y</code>.
</p><p>
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 />
<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
a 'wither' is generated for each field (even non-final fields).
</p><p>
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.
</p><p>
<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).
</p>
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<div class="snippets">
<div class="pre">
<h3>With Lombok</h3>
<div class="snippet">@HTML_PRE@</div>
</div>
<div class="sep"></div>
<div class="post">
<h3>Vanilla Java</h3>
<div class="snippet">@HTML_POST@</div>
</div>
</div>
<div style="clear: left;"></div>
<div class="overview confKeys">
<h3>Supported configuration keys:</h3>
<dl>
<dt><code>lombok.wither.flagUsage</code> = [<code>warning</code> | <code>error</code>] (default: not set)</dt>
<dd>Lombok will flag any usage of <code>@Wither</code> as a warning or error if configured.</dd>
</dl>
</div>
<div class="overview">
<h3>Small print</h3><div class="smallprint">
<p>
Withers cannot be generated for static fields because that makes no sense.
</p><p>
Withers can be generated for abstract classes, but this generates an abstract method with the appropriate signature.
</p><p>
When applying <code>@Wither</code> to a type, static fields and fields whose name start with a $ are skipped.
</p><p>
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.
Then, <code>with</code> is prefixed.
</p><p>
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>
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
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.
</p><p>
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.
</p><p>
Any annotations named <code>@NonNull</code> (case insensitive) on the field are interpreted as: This field must not ever hold
<em>null</em>. Therefore, these annotations result in an explicit null check in the generated wither. Also, these
annotations (as well as any annotation named <code>@Nullable</code> or <code>@CheckForNull</code>) are copied to wither parameter.
</p>
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