@Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        Pair other = (Pair) obj;
        if (this.first == null) {
            if (other.first != null) {
                return false;
            }
        }
        else if (!this.first.equals(other.first)) {
            return false;
        }
        if (this.second == null) {
            if (other.second != null) {
                return false;
            }
        }
        else if (!this.second.equals(other.second)) {
            return false;
        }
        return true;
    }