Custom form in Drupal 8

resume/resume.info.yml

name: Resume
description: A Resume form to enter user details.
core: 8.x
package: Custom
type: module

resume/resume.routing.yml

resume.form:
path: '/resume/myform'
    defaults:
        _title: 'Application form'
        _form: '\Drupal\resume\Form\ResumeForm'
    requirements:
        _permission: 'access content'

resume/src/Form/ResumeForm.php

 'textfield',
      '#title' => t('Candidate Name:'),
      '#required' => TRUE,
    );
    $form['candidate_mail'] = array(
      '#type' => 'email',
      '#title' => t('Email ID:'),
      '#required' => TRUE,
    );
    $form['candidate_number'] = array (
      '#type' => 'tel',
      '#title' => t('Mobile no'),
    );
    $form['candidate_dob'] = array (
      '#type' => 'date',
      '#title' => t('DOB'),
      '#required' => TRUE,
    );
    $form['candidate_gender'] = array (
      '#type' => 'select',
      '#title' => ('Gender'),
      '#options' => array(
        'Female' => t('Female'),
        'male' => t('Male'),
      ),
    );
    $form['candidate_confirmation'] = array (
      '#type' => 'radios',
      '#title' => ('Are you above 18 years old?'),
      '#options' => array(
        'Yes' =>t('Yes'),
        'No' =>t('No')
      ),
    );
    $form['candidate_copy'] = array(
      '#type' => 'checkbox',
      '#title' => t('Send me a copy of the application.'),
    );
    $form['actions']['#type'] = 'actions';
    $form['actions']['submit'] = array(
      '#type' => 'submit',
      '#value' => $this->t('Save'),
      '#button_type' => 'primary',
    );
    return $form;
  }
  /**
   * {@inheritdoc}
   */
    public function validateForm(array &$form, FormStateInterface $form_state) {
      if (strlen($form_state->getValue('candidate_number')) < 10) {
        $form_state->setErrorByName('candidate_number', $this->t('Mobile number is too short.'));
      }
    }
  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) {
   // drupal_set_message($this->t('@can_name ,Your application is being submitted!', array('@can_name' => $form_state->getValue('candidate_name'))));
    foreach ($form_state->getValues() as $key => $value) {
      drupal_set_message($key . ': ' . $value);
    }
   }
}