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Diffstat (limited to 'website2/templates/features/EqualsAndHashCode.html')
| -rw-r--r-- | website2/templates/features/EqualsAndHashCode.html | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/website2/templates/features/EqualsAndHashCode.html b/website2/templates/features/EqualsAndHashCode.html index 91a9cb70..3c11367f 100644 --- a/website2/templates/features/EqualsAndHashCode.html +++ b/website2/templates/features/EqualsAndHashCode.html @@ -5,9 +5,9 @@ <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/> + If applying <code>@EqualsAndHashCode</code> to a class that extends another, this feature gets a bit trickier. Normally, auto-generating an <code>equals</code> and <code>hashCode</code> method for such classes is a bad idea, as the superclass also defines fields, which also need equals/hashCode code but this code will not be generated. 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. If you have an explicit superclass you are forced to supply some value for <code>callSuper</code> to acknowledge that you've considered it; failure to do so results in a warning. </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. + 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. You can also use the <code>lombok.equalsAndHashCode.callSuper</code> config key. </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="https://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><p> @@ -23,6 +23,10 @@ </dt><dd> If set to <code>true</code>, lombok will access fields directly instead of using getters (if available) when generating <code>equals</code> and <code>hashCode</code> methods. The annotation parameter '<code>doNotUseGetters</code>', if explicitly specified, takes precedence over this setting. </dd><dt> + <code>lombok.equalsAndHashCode.callSuper</code> = [<code>call</code> | <code>skip</code> | <code>warn</code>] (default: warn) + </dt><dd> + If set to <code>call</code>, lombok will generate calls to the superclass implementation of <code>hashCode</code> and <code>equals</code> if your class extends something. If set to <code>skip</code> no such calls are generated. The default behaviour is like <code>skip</code>, with an additional warning. + </dd><dt> <code>lombok.equalsAndHashCode.flagUsage</code> = [<code>warning</code> | <code>error</code>] (default: not set) </dt><dd> Lombok will flag any usage of <code>@EqualsAndHashCode</code> as a warning or error if configured. |