Doctor.java

 @Override
    public int hashCode() {
        int result = 1;

        result = result * 16 + (this.person == null ? 21 : this.person.hashCode());
        result = result * 16 + (this.visits == null ? 21 : this.visits.hashCode());
        result = result * 16 + (this.specialization == null ? 21 : this.specialization.hashCode());
        result = result * 16 + (this.salary == null ? 21 : this.salary.hashCode());

        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if(obj == this) {
            return true;
        } else if(obj == null) {
            return false;
        } else if(!(obj instanceof Doctor)) {
            return false;
        } else {
            Doctor other = (Doctor) obj;

            Person thisPerson = this.person;
            Person otherPerson = other.getPerson();
            if(thisPerson == null) {
                if(otherPerson != null) {
                    return false;
                }
            } else if(!thisPerson.equals(otherPerson)) {
                return false;
            }

            List<Visit> thisVisits = this.visits;
            List<Visit> otherVisits = other.getVisits();
            if(thisVisits == null) {
                if(otherVisits != null) {
                    return false;
                }
            } else if(!thisVisits.equals(otherVisits)) {
                return false;
            }

            String thisSpecialization = this.specialization;
            String otherSpecialization = other.getSpecialization();
            if(thisSpecialization == null) {
                if(otherSpecialization != null) {
                    return false;
                }
            } else if(!thisSpecialization.equals(otherSpecialization)) {
                return false;
            }

            Integer thisSalary = this.salary;
            Integer otherSalary = other.getSalary();
            if(thisSalary == null) {
                if(otherSalary != null) {
                    return false;
                }
            } else if(!thisSalary.equals(otherSalary)) {
                return false;
            }
        }
        return true;
    }