Vanilla Java
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Any class definition may be annotated with @EqualsAndHashCode to let lombok generate implementations of the equals(Object other) and hashCode() methods. By default, it'll use all non-static, non-transient fields, but you can exclude more fields by naming them in the optional exclude parameter to the annotation. Alternatively, you can specify exactly which fields you wish to be used by naming them in the of parameter.
If applying @EqualsAndHashCode to a class that extends another, this feature gets a bit trickier. Normally, auto-generating an equals and hashCode 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 callSuper to true, you can include the equals and hashCode methods of your superclass in the generated methods. For hashCode, the result of super.hashCode() is included in the hash algorithm, and for equals, 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 equals implementations handle this situation properly. However, lombok-generated equals implementations do handle this situation properly, so you can safely call your superclass equals if it, too, has a lombok-generated equals method. If you have an explicit superclass you are forced to supply some value for callSuper to acknowledge that you've considered it; failure to do so results in a warning.
Setting callSuper to true when you don't extend anything (you extend java.lang.Object) is a compile-time error, because it would turn the generated equals() and hashCode() implementations into having the same behaviour as simply inheriting these methods from java.lang.Object: only the same object will be equal to each other and will have the same hashCode. Not setting callSuper to true 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
callSuper chaining facility.
NEW in Lombok 0.10: Unless your class is final and extends java.lang.Object, lombok generates a canEqual 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: How to Write an Equality Method in Java.
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 canEqual if you change equals and hashCode.
NEW in Lombok 1.14.0: To put annotations on the other parameter of the equals (and, if relevant, canEqual) method, you can use onParam=@__({@AnnotationsHere}). Be careful though! This is an experimental feature. For more details see the documentation on the onX feature.
lombok.equalsAndHashCode.doNotUseGetters = [true | false] (default: false)true, lombok will access fields directly instead of using getters (if available) when generating equals and hashCode methods. The annotation parameter 'doNotUseGetters', if explicitly specified, takes precedence over this setting.lombok.equalsAndHashCode.flagUsage = [warning | error] (default: not set)@EqualsAndHashCode as a warning or error if configured.
Arrays are 'deep' compared/hashCoded, which means that arrays that contain themselves will result in StackOverflowErrors. However, this behaviour is no different from e.g. ArrayList.
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.
For the purposes of equality, 2 NaN (not a number) values for floats and doubles are considered equal, eventhough 'NaN == NaN' would return false. This is analogous to java.lang.Double's equals method, and is in fact required to ensure that comparing an object to an exact copy of itself returns true for equality.
If there is any method named either hashCode or equals, regardless of return type, no methods will be generated, and a warning is emitted instead. These 2 methods need to be in sync with each other, which lombok cannot guarantee unless it generates all the methods, hence you always get a warning if one or both of the methods already exist. You can mark any method with @lombok.experimental.Tolerate to hide them from lombok.
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.
Having both exclude and of generates a warning; the exclude parameter will be ignored in that case.
By default, any variables that start with a $ symbol are excluded automatically. You can only include them by using the 'of' parameter.
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:
@EqualsAndHashCode(doNotUseGetters = true)