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<title>@XArgsConstructor</title>
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<div class="header"><a href="../index.html">Project Lombok</a></div>
<h1>@NoArgsConstructor, @RequiredArgsConstructor, @AllArgsConstructor</h1>
<div class="byline">Constructors made to order: Generates constructors that take no arguments, one argument per final / non-null field, or one argument for every field.</div>
<div class="overview">
<h3>Overview</h3>
<p>
This set of 3 annotations generate a constructor that will accept 1 parameter for certain fields, and simply assigns this parameter to the field.
</p><p>
<code>@NoArgsConstructor</code> will generate a constructor with no parameters. If this is not possible (because of final fields), a compiler error will result instead.
For fields with constraints, such as <code>@NonNull</code> fields, <em>no</em> check or assignment is generated, so be aware that these constraints may then not be
fulfilled until those fields are properly initialized later. Certain java constructs, such as hibernate and the Service Provider Interface require a no-args constructor.
This annotation is useful primarily in combination with either <code>@Data</code> or one of the other constructor generating annotations.
</p><p>
<code>@RequiredArgsConstructor</code> generates a constructor with 1 parameter for each field that requires special handling. All <code>final</code> fields get a parameter,
as well as any fields that are marked as <code>@NonNull</code> that aren't initialized where they are declared. For those fields marked with <code>@NonNull</code>, an explicit
null check is also generated. The constructor will throw a <code>NullPointerException</code> if any of the parameters intended for the fields marked with <code>@NonNull</code>
contain <code>null</code>. The order of the parameters match the order in which the fields appear in your class.
</p><p>
<code>@AllArgsConstructor</code> generates a constructor with 1 parameter for each field in your class. Fields marked with <code>@NonNull</code> result in null checks on
those parameters.
</p><p>
Each of these annotations allows an alternate form, where the generated constructor is always private, and an additional static factory method that wraps around the
private constructor is generated. This mode is enabled by supplying the <code>staticName</code> value for the annotation, like so: <code>@RequiredArgsConstructor(staticName = "of")</code>.
Such a static factory method will infer generics, unlike a normal constructor. This means your API users get write <code>MapEntry.of("foo", 5)</code> instead of the much longer
<code>new MapEntry<String, Integer>("foo", 5)</code>.
</p><p>
Static fields are skipped by these annotations. Also, a <code>@java.beans.ConstructorProperties</code> annotation is added for all constructors with at least 1 argument,
which allows bean editor tools to call the generated constructors. <code>@ConstructorProperties</code> is now in Java 1.6, which means that if your code is intended for
compilation on Java 1.5, a compiler error will occur. <em>Running</em> on a JVM 1.5 should be no problem (the annotation will be ignored). To suppress the generation of
the <code>@ConstructorProperties</code> annotation, add a parameter to your annotation: <code>@AllArgsConstructor(suppressConstructorProperties=true)</code>. However,
as java 1.5, which has already been end-of-lifed, fades into obscurity, this parameter will eventually be removed. It has also been marked deprecated for this reason.
</p><p>
Unlike most other lombok annotations, the existence of an explicit constructor does not stop these annotations from generating their own constructor. This means you can write
your own specialized constructor, and let lombok generate the boilerplate ones as well. If a conflict arises (one of your constructors ends up with the same
signature as one that lombok generates), a compiler error will occur.
</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">
<h3>Small print</h3><div class="smallprint">
<p>
Even if a field is explicitly initialized with <code>null</code>, lombok will consider the requirement to avoid null as fulfilled, and will <em>NOT</em> consider
the field as a 'required' argument. The assumption is that if you explicitly assign <code>null</code> to a field that you've also marked as <code>@NonNull</code>
signals you must know what you're doing.
</p><p>
The <code>@java.beans.ConstructorProperties</code> annotation is never generated for a constructor with no arguments. This also explains why <code>@NoArgsConstructor</code>
lacks the <code>suppressConstructorProperties</code> annotation method. The <code>@ConstructorProperties</code> annotation is also omitted for private constructors. The
generated static factory methods also do not get <code>@ConstructorProperties</code>, as this annotation can only be added to real constructors.
</p><p>
<code>@XArgsConstructor</code> can also be used on an enum definition. The generated constructor will always be
private, because non-private constructors aren't legal in enums. You don't have to specify <code>AccessLevel.PRIVATE</code>.
</p><p>
While <code>suppressConstructorProperties</code> has been marked deprecated in anticipation of a world where all java environments have the
<code>@ConstructorProperties</code> annotation available, first GWT 2.2 and Android 2.3.3, which do not (yet) have this annotation, will have
to be ancient history before this annotation parameter will be removed.
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