Calling two namespaces for formbuilder and controller in d8 I have a d8 form as follows ,and am calling a new class by including the file in the formbuilder class , But its throwing me a class not found error ,although am including the class in the form builder and namespace in the calling class .

    namespace Drupal\module_name\Form;

    use Drupal\Core\Form\ConfigFormBase;
    use Drupal\Core\Form\FormStateInterface;
    use Drupal\Core\Form\FormState;

    //included class 
    require_once './' . drupal_get_path('module', 'gasf') . '/includes/config_class.inc';


    class ClassName extends ConfigFormBase {

      public function getFormId() {
        return 'class_name';
      }
    /**
     * General form for switching all nodes from one user to another.
     */
      public function buildForm(array $form, FormStateInterface $form_state) {
      $Config = new ConfigClass();
      $operations = array(
          'IP -&gt; vm name',
          'vm name -&gt; IP',
      );


    $argument = empty($argument) ? '' : $argument;
    $operations = empty($operations) ? '' : $operations;

    $form['argument'] = array(
        '#type' =&gt; 'textfield',
        '#title' =&gt; t('Enter argument here'),
        '#default_value' =&gt; $argument,
        '#description' =&gt; t('Depending on operation: tcp/ip adress or vm name'),
    );

    $form['operation'] = array(
        '#type' =&gt; 'select',
        '#title' =&gt; t('Operation:'),
        '#options' =&gt; $operations,
        '#description' =&gt; t(''),
    );

    $form['submit_lookup'] = array(
        '#type' =&gt; 'submit',
        '#value' =&gt; t('Lookup'),
    );

    return $form;      
}


and in the config_class.inc i have 

namespace Drupal\module_name\Controller;
namespace Drupal\module_name\Form;

class ConfigClass {

}


But its calling the latest namespace only , that is when i use namespace Drupal\module_name\Form; its working properly , But it wont take effect the namespace Drupal\module_name\Controller; namespace  .That will through error on calling the class from controller ! . How can i use the namespaces for both formbuilder and controller class ? Or is there any other workarounds ?
A class can only be in one namespace. There's never a scenario when a class being in two namespaces could be useful, and the language doesn't allow it.

I have no idea what you're trying to achieve, there's no mention of that in your question, so again I'll just reiterate (3rd time now!) that you should learn what namespaces are, what autoloading is, what PSR4 is, and how to use them. Otherwise you're just going to spend your time banging your head against these trivial PHP language issues, and get very little done.