Overriding equals() & hashCode() in sub classes … considering super fields

Question

Is there a specific rule on how Overriding equals() & hashCode() in sub classes considering super fields ?? k

Answer 1

It's worth noting that the IDE auto generation maybe has taken into consideration super class，just provided that the equals() and hashCode() of super class exists yet. That is, should auto generate these two functions of super first, and then auto generate of the child. I got below right example under Intellj Idea:

@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    if (!super.equals(o)) return false;

    TActivityWrapper that = (TActivityWrapper) o;

    return data != null ? data.equals(that.data) : that.data == null;
}

@Override
public int hashCode() {
    int result = super.hashCode();
    result = 31 * result + (data != null ? data.hashCode() : 0);
    return result;
}

The problem happens just when you don't auto generate super's in first. Please check above under Netbeans.