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<#import "../_features.html" as f>
<@f.scaffold title="@Wither" logline="Immutable 'setters' - methods that create a clone but with one changed field.">
<@f.history>
<p>
@Wither was introduced as experimental feature in lombok v0.11.4.
</p>
</@f.history>
<@f.experimental>
<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.
</@f.experimental>
<@f.overview>
<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="/features/GetterSetter"><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="/features/GetterSetter"><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="/features/experimental/onX">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>
</@f.overview>
<@f.snippets name="experimental/Wither" />
<@f.confKeys>
<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>
</@f.confKeys>
<@f.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>
</@f.smallPrint>
</@f.scaffold>
|
