@Override
    public int eval()
    {
        if ( m_op == Op.PLUS )
            return m_exp1.eval() + m_exp2.eval();
        else if ( m_op == Op.MINUS )
            return m_exp1.eval() + m_exp2.eval();
        else if ( m_op == Op.TIMES )
            return m_exp1.eval() * m_exp2.eval();
        else
            return m_exp1.eval() / m_exp2.eval();
    }