Lombok inheritance with @EqualsAndHashCode

Question

I have a class which extends a parent class using @EqualsAndHashCode. I am getting a compilation error with Lombok 1.16.0 and Java 8

@EqualsAndHashCode(doNotUseGetters = true, of = { "propertyA", "propertyB" }) public class Parent {...}

@EqualsAndHashCode(callSuper = true, doNotUseGetters = true, of = { "propertyC", "propertyD" }) public class Child extends Parent {...}

The error is...

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project granger: Compilation failure [ERROR] /Users/sarah/src/main/java/com/xxx/Child.java:[26,1] canEqual(java.lang.Object) in com.xxx.Child cannot override canEqual(java.lang.Object) in com.yyy.Parent [ERROR] attempting to assign weaker access privileges; was public [ERROR] attempting to assign weaker access privileges; was public

Is there any best practice around inheritance and @EqualsAndHashCode and Lombok that I am abusing? Or any way around this?

Answer 1

Even if you made this build you would end up with a broken equals method, because it won't be symmetric ( parent.equals(child) if they have the same values in the parent fields, but never child.equals(parent) ). It's been a while since I used Lombok, but scala case classes (which are more or less equivalent in this regard) cannot extend other case classes for this reason.

Think very carefully about what Parent and Child represent. Is Child really Liskov-substitutable for Parent ? If so, it might be better to inherit the definition of equals and hashCode from Parent , and not try to redefine them in Child at all; if not, it might be better to extract the common functionality into a common superclass which both Parent and Child extend, rather than having them as parent and child.

Answer 2

It seems the classes are in different artifacts or you made an incremental build.

Before 1.14 canEqual was public , since then it's protected .

If you make a clean and / or compile Parent using Lombok 1.16 it should work.