Defining a Symfony form in a separate class - http://www.symfonycentral.com

ArticleType.php

<?php 
// src/MyCompany/BlogBundle/Form/Type/ArticleType.php

namespace MyCompany\BlogBundle\Form\Type;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\FormBuilder;

class ArticleType extends AbstractType
{
    public function buildForm(FormBuilder $builder, array $options)
    {
        $builder->add('title', 'text');
        $builder->add('body', 'textarea');
    }

    public function getName()
    {
        /* The name should be a unique identifier for the form */
        return 'article';
    }

    public function getDefaultOptions(array $options)
    {
        /* If this form corresponds to an Entity, we should include it here */
        return array(
            'data_class' => 'MyCompany\BlogBundle\Entity\Article',
        );
    }
}