JAVA : How to remove duplicates from list using stream

user_7193486 0
Viewed 202

I want to remove duplicates from a list based on a property(mail) of the items in the list.
I did this : 

acteurs = acteurs.stream().distinct().collect(Collectors.toList());

The equals method of Acteur

@Override
public boolean equals(Object o) {
    if (this.getMail().equals(((Acteur)o).getMail())) {
        return true;
    }
    if (this == o) {
        return true;
    }
    if (o == null || getClass() != o.getClass()) {
        return false;
    }
    Acteur acteur = (Acteur) o;
    if(acteur.id == null || id == null) {
        return false;
    }
    return Objects.equals(id, acteur.id);
}

The equals method should be called during the instruction 

acteurs = acteurs.stream().distinct().collect(Collectors.toList());

But it isn't.
Where am I wrong?

UPDATE :
My solution : 

List<Acteur> dto3s =acteurs.stream()
            .collect(Collectors.collectingAndThen(
                Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(Acteur:: getMail))),
                ArrayList::new));
java-stream list java
3 Answers

You broke equals/hashCode contract.

You need to implement hashCode according to requirements.

user_36569040

you can use the following solution, where you create a map by the distinct key mail and get the map's values

acteurs.stream().collect(Collectors.toMap(a -> a.getMail(), Function.identity(), (a1, a2) -> a1)).values();

the third arg (a1, a2) -> a1 means that whenever it get a conflicts i.e need to add to the map an entry (key,value) with the same key it will use the map's current value, i.e no-op

keep in mind, this will only compare by mail property, if you want to compare by a more complex way using the map logic, you might need to implement hash() and equals() properly

user_52353920

Your equals method seems not correct because you need to "return false" if the "if condition" is not fulfilled

user_41018420
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