Hashcode optimisation

[tom-zoladz]

GF found in J.Bloch books that current hashCode method is not recommended due to low efficiency. Current solution for Entry class:

@Override
public int hashCode() {
    return Objects.hash(key, value, type, info);
}

Consider to use:

    @Override
    public int hashCode() {
        return key != null ? key.hashCode() : 0;
    }

because key parameter looks like to be unique.

Consider to update hashcode for other classes in similar way.