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<div class="header"><a href="../index.html">Project Lombok</a></div>
<h1>@EqualsAndHashCode</h1>
<div class="byline">Equality made easy: Generates <code>hashCode</code> and <code>equals</code> implementations from the fields of your object.</div>
<div class="overview">
<h3>Overview</h3>
<p>
Any class definition may be annotated with <code>@EqualsAndHashCode</code> to let lombok generate implementations of the
<code>equals(Object other)</code> and <code>hashCode()</code> methods. By default, it'll use all non-static, non-transient
fields, but you can exclude more fields by naming them in the optional <code>exclude</code> parameter to the annotation.
Alternatively, you can specify exactly which fields you wish to be used by naming them in the <code>of</code> parameter.
</p><p>
By setting <code>callSuper</code> to <em>true</em>, you can include the <code>equals</code> and <code>hashCode</code> methods of your superclass in the generated methods.
For <code>hashCode</code>, the result of <code>super.hashCode()</code> is included in the hash algorithm, and for <code>equals</code>, the generated method will return
false if the super implementation thinks it is not equal to the passed in object. Be aware that not all <code>equals</code> implementations handle this situation properly.
However, lombok-generated <code>equals</code> implementations <strong>do</strong> handle this situation properly, so you can safely call your superclass equals if it, too,
has a lombok-generated <code>equals</code> method.<br />
</p><p>
Setting <code>callSuper</code> to <em>true</em> when you don't extend anything (you extend <code>java.lang.Object</code>) is a compile-time error, because it would turn
the generated <code>equals()</code> and <code>hashCode()</code> implementations into having the same behaviour as simply inheriting these methods from <code>java.lang.Object</code>:
only the same object will be equal to each other and will have the same hashCode.
Not setting <code>callSuper</code> to <em>true</em> when you extend another class generates a warning, because unless the superclass has no (equality-important) fields, lombok
cannot generate an implementation for you that takes into account the fields declared by your superclasses. You'll need to write your own implementations, or rely on the
<code>callSuper</code> chaining facility.
</p><p>
<em>NEW in Lombok 0.10: </em>Unless your class is <code>final</code> and extends <code>java.lang.Object</code>, lombok generates a <code>canEqual</code> method
which means JPA proxies can still be equal to their base class, but subclasses that add new state don't break the equals contract. The complicated reasons for
why such a method is necessary are explained in this paper: <a href="http://www.artima.com/lejava/articles/equality.html">How to Write an Equality Method in Java</a>.
If all classes in a hierarchy are a mix of scala case classes and classes with lombok-generated equals methods, all equality will 'just work'.
If you need to write your own equals methods, you should always override <code>canEqual</code> if you change <code>equals</code> and <code>hashCode</code>.
</p>
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<h3>With Lombok</h3>
<div class="snippet">@HTML_PRE@</div>
</div>
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<h3>Vanilla Java</h3>
<div class="snippet">@HTML_POST@</div>
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<div style="clear: left;"></div>
<div class="overview">
<h3>Small print</h3><div class="smallprint">
<p>
Arrays are 'deep' compared/hashCoded, which means that arrays that contain themselves will result in <code>StackOverflowError</code>s. However,
this behaviour is no different from e.g. <code>ArrayList</code>.
</p><p>
You may safely presume that the hashCode implementation used will not change between versions of lombok, however this guarantee is not set in stone;
if there's a significant performance improvement to be gained from using an alternate hash algorithm, that will be substituted in a future version.
</p><p>
For the purposes of equality, 2 <code>NaN</code> (not a number) values for floats and doubles are considered equal, eventhough 'NaN == NaN' would
return false. This is analogous to <code>java.lang.Double</code>'s equals method, and is in fact required to ensure that comparing an object
to an exact copy of itself returns <code>true</code> for equality.
</p><p>
If there is <em>any</em> method named either <code>hashCode</code> or <code>equals</code>, regardless of parameters or return type,
that method will not be generated, and a warning is emitted instead. <code>hashCode</code> and <code>equals</code> need to be in sync with
each other, which lombok cannot guarantee if it is only generating one of the two methods, hence you always get a warning if one <em>or</em> both
of the methods already exist.
</p><p>
Attempting to exclude fields that don't exist or would have been excluded anyway (because they are static or transient) results in warnings on the named fields.
You therefore don't have to worry about typos.
</p><p>
Having both <code>exclude</code> and <code>of</code> generates a warning; the <code>exclude</code> parameter will be ignored in that case.
</p><p>
By default, any variables that start with a $ symbol are excluded automatically. You can only include them by using the 'of' parameter.
</p><p>
If a getter exists for a field to be included, it is called instead of using a direct field reference. This behaviour can be suppressed:<br />
<code>@EqualsAndHashCode(doNotUseGetters = true)</code>
</p>
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