Lombok @EqualsAndHashCode on a class which has a list

Question

@EqualsAndHashcode
class MyClass {
    String property1;
    List<NewClass> newClassList;
}

@EqualsAndHashcode
class NewClass {
    String abc;
    String xyz;
}

If I compare two objects of MyClass (its annotated with @EqualsAndHashcode) for equality, will order of newClassList property be checked ?

Thanks for the response. How can I make sure that order is not compared. Can I do any tweaking with EqualsAndHashcode or should I use a separate comparator for properties which are list. — Sarthak Shah, Feb 18 '22 at 20:25

score 3 · Accepted Answer · answered Feb 18 '22 at 20:43

By using @EqualsAndHashcode it will propagate to use newClassList.equals(..) method which according to java doc

Interface List

boolean equals(Object o) Compares the specified object with this list for equality. Returns true if and only if the specified object is also a list, both lists have the same size, and all corresponding pairs of elements in the two lists are equal. (Two elements e1 and e2 are equal if (e1==null ? e2==null : e1.equals(e2)).) In other words, two lists are defined to be equal if they contain the same elements in the same order. This definition ensures that the equals method works properly across different implementations of the List interface.

If you want a custom functionality where list does not check the order then you have to drop @EqualsAndHashcode and provide your own equals method based on what you want.

The functionality that you want would be in a simple way

(list1 != null && list2 != null && list1.size() == list2.size() && list1.containsAll(list2) && list2.containsAll(list1) ) || (list1 == null && list2 == null)

This would lead us to the following equals method

@Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        NewClass newClass = (NewClass) o;
        return Objects.equals(property1, newClass.property1) &&
                ((newClassList != null && newClass.newClassList != null && newClassList.size() == newClass.newClassList.size() && newClassList.containsAll(newClass.newClassList) && newClass.newClassList.containsAll(newClassList) ) || (newClassList == null && list2 == null));
               
    }

Don't forget also to manually override hashcode method as well.

Lombok @EqualsAndHashCode on a class which has a list

1 Answers1