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@Wither

Immutable 'setters' - methods that create a clone but with one changed field.

Since

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

Experimental

- Experimental because: -

Still not sure that @Wither is an appropriate name for this feature.
Should there be an option to supply a way of cloning the input somehow?
Should the way that the clone is created by configurable?
Should we replace @Wither entirely with a builder class?

- Current status: neutral - More feedback requires on the items in the above list before promotion to the main package is warranted. -

Overview

- 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 @Wither generates: a withFieldName(newValue) method which produces a clone - except for the new value for the associated field. -

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

- Like @Setter, you can specify an access level in case you want the generated wither to be something other than public:
- @Wither(level = AccessLevel.PROTECTED). Also like @Setter, you can also put a @Wither annotation on a type, which means - a 'wither' is generated for each field (even non-final fields). -

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

- NEW in lombok v1.12.0: javadoc on the field will now be copied to generated withers. Normally, all text is copied, and @param is moved to the wither, whilst @return 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 WITHER. 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, @return and @param stripping / copying for that section is no longer done (move the @param line into the section). -

With Lombok

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Vanilla Java

@HTML_POST@

Supported configuration keys:

lombok.wither.flagUsage = [warning | error] (default: not set): Lombok will flag any usage of @Wither as a warning or error if configured.

Small print

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

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

- When applying @Wither to a type, static fields and fields whose name start with a $ are skipped. -

- 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, with is prefixed. -

- No method is generated if any method already exists with the same name (case insensitive) and same parameter count. For example, withX(int x) - will not be generated if there's already a method withX(String... x) 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. -

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

- Any annotations named @NonNull (case insensitive) on the field are interpreted as: This field must not ever hold - null. Therefore, these annotations result in an explicit null check in the generated wither. Also, these - annotations (as well as any annotation named @Nullable or @CheckForNull) are copied to wither parameter. -

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