Lombok features - @EqualsAndHashCode

Equality made easy: Generates hashCode and equals implementations from the fields of your object.

Overview

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 modify which fields are used (and even specify that the output of various methods is to be used) by marking type members with @EqualsAndHashCode.Include or @EqualsAndHashCode.Exclude. Alternatively, you can specify exactly which fields or methods you wish to be used by marking them with @EqualsAndHashCode.Include and using @EqualsAndHashCode(onlyExplicitlyIncluded = true).

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 forequals, 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. You can also use the lombok.equalsAndHashCode.callSuper config key.

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.

With Lombok

import lombok.EqualsAndHashCode; @EqualsAndHashCode public class EqualsAndHashCodeExample {   private transient int transientVar = 10;   private String name;   private double score;   @EqualsAndHashCode.Exclude private Shape shape = new Square(5, 10);   private String[] tags;   @EqualsAndHashCode.Exclude private int id;      public String getName() {     return this.name;   }      @EqualsAndHashCode(callSuper=true)   public static class Square extends Shape {     private final int width, height;          public Square(int width, int height) {       this.width = width;       this.height = height;     }   } }

Vanilla Java

import java.util.Arrays; public class EqualsAndHashCodeExample {   private transient int transientVar = 10;   private String name;   private double score;   private Shape shape = new Square(5, 10);   private String[] tags;   private int id;      public String getName() {     return this.name;   }      @Override public boolean equals(Object o) {     if (o == this) return true;     if (!(o instanceof EqualsAndHashCodeExample)) return false;     EqualsAndHashCodeExample other = (EqualsAndHashCodeExample) o;     if (!other.canEqual((Object)this)) return false;     if (this.getName() == null ? other.getName() != null : !this.getName().equals(other.getName())) return false;     if (Double.compare(this.score, other.score) != 0) return false;     if (!Arrays.deepEquals(this.tags, other.tags)) return false;     return true;   }      @Override public int hashCode() {     final int PRIME = 59;     int result = 1;     final long temp1 = Double.doubleToLongBits(this.score);     result = (result*PRIME) + (this.name == null ? 43 : this.name.hashCode());     result = (result*PRIME) + (int)(temp1 ^ (temp1 >>> 32));     result = (result*PRIME) + Arrays.deepHashCode(this.tags);     return result;   }      protected boolean canEqual(Object other) {     return other instanceof EqualsAndHashCodeExample;   }      public static class Square extends Shape {     private final int width, height;          public Square(int width, int height) {       this.width = width;       this.height = height;     }          @Override public boolean equals(Object o) {       if (o == this) return true;       if (!(o instanceof Square)) return false;       Square other = (Square) o;       if (!other.canEqual((Object)this)) return false;       if (!super.equals(o)) return false;       if (this.width != other.width) return false;       if (this.height != other.height) return false;       return true;     }          @Override public int hashCode() {       final int PRIME = 59;       int result = 1;       result = (result*PRIME) + super.hashCode();       result = (result*PRIME) + this.width;       result = (result*PRIME) + this.height;       return result;     }          protected boolean canEqual(Object other) {       return other instanceof Square;     }   } }

Supported configuration keys:

lombok.equalsAndHashCode.doNotUseGetters = [true | false] (default: false)

If set to 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.callSuper = [call | skip | warn] (default: warn)

If set to call, lombok will generate calls to the superclass implementation of hashCode and equals if your class extends something. If set to skip no such calls are generated. The default behaviour is like skip, with an additional warning.

lombok.equalsAndHashCode.flagUsage = [warning | error] (default: not set)

Lombok will flag any usage of @EqualsAndHashCode as a warning or error if configured.