@Override
    public boolean equals(Object obj)
    {
        if (this == obj)
        {
            return true;
        }
        if (obj == null)
        {
            return false;
        }
        if (!(obj instanceof Bigram))
        {
            return false;
        }
        Bigram other = (Bigram) obj;
        if (word1 == null)
        {
            if (other.word1 != null)
            {
                return false;
            }
        }
        else if (!word1.equals(other.word1))
        {
            return false;
        }
        if (word2 == null)
        {
            if (other.word2 != null)
            {
                return false;
            }
        }
        else if (!word2.equals(other.word2))
        {
            return false;
        }
        return true;
    }