abstract class ConditionPluginBase

Language.php in drupal/core/modules/language/lib/Drupal/language/Plugin/Condition/Language.php

Contains \Drupal\language\Plugin\Condition\Language.

NodeType.php in drupal/core/modules/node/lib/Drupal/node/Plugin/Condition/NodeType.php

Contains \Drupal\node\Plugin\Condition\NodeType.

Php.php in drupal/core/modules/php/lib/Drupal/php/Plugin/Condition/Php.php

Contains \Drupal\php\Plugin\Condition\Php.

abstract class ConditionPluginBase extends ExecutablePluginBase implements ConditionInterface {

  /**
   * Implements \Drupal\Core\Form\FormInterface::getFormID().
   */
  public function getFormID() {
    $definition = $this
      ->getPluginDefinition();
    return implode('_', array(
      $definition['module'],
      $definition['id'],
      'condition',
    ));
  }

  /**
   * Implements \Drupal\condition\Plugin\ConditionInterface::isNegated().
   */
  public function isNegated() {
    return !empty($this->configuration['negate']);
  }

  /**
   * Implements \Drupal\Core\Form\FormInterface::buildForm().
   */
  public function buildForm(array $form, array &$form_state) {
    $form['negate'] = array(
      '#type' => 'checkbox',
      '#title' => t('Negate the condition.'),
      '#default_value' => isset($this->configuration['negate']) ? $this->configuration['negate'] : FALSE,
    );
    return $form;
  }

  /**
   * Implements \Drupal\Core\Form\FormInterface::validateForm().
   */
  public function validateForm(array &$form, array &$form_state) {
  }

  /**
   * Implements \Drupal\Core\Form\FormInterface::submitForm().
   */
  public function submitForm(array &$form, array &$form_state) {
    $this->configuration['negate'] = $form_state['values']['negate'];
  }

  /**
   * Implements \Drupal\Core\Executable\ExecutablePluginBase::execute().
   */
  public function execute() {
    return $this->executableManager
      ->execute($this);
  }

}