diff --git a/core/lib/Drupal/Core/Datetime/DateFormatter.php b/core/lib/Drupal/Core/Datetime/DateFormatter.php
index a1cd4a0..be23303 100644
--- a/core/lib/Drupal/Core/Datetime/DateFormatter.php
+++ b/core/lib/Drupal/Core/Datetime/DateFormatter.php
@@ -21,7 +21,7 @@
  *
  * @ingroup i18n
  */
-class DateFormatter {
+class DateFormatter implements DateFormatterInterface {
   use StringTranslationTrait;
 
   /**
@@ -104,34 +104,7 @@ public function __construct(EntityManagerInterface $entity_manager, LanguageMana
   }
 
   /**
-   * Formats a date, using a date type or a custom date format string.
-   *
-   * @param int $timestamp
-   *   A UNIX timestamp to format.
-   * @param string $type
-   *   (optional) The format to use, one of:
-   *   - One of the built-in formats: 'short', 'medium',
-   *     'long', 'html_datetime', 'html_date', 'html_time',
-   *     'html_yearless_date', 'html_week', 'html_month', 'html_year'.
-   *   - The name of a date type defined by a date format config entity.
-   *   - The machine name of an administrator-defined date format.
-   *   - 'custom', to use $format.
-   *   Defaults to 'medium'.
-   * @param string $format
-   *   (optional) If $type is 'custom', a PHP date format string suitable for
-   *   input to date(). Use a backslash to escape ordinary text, so it does not
-   *   get interpreted as date format characters.
-   * @param string|null $timezone
-   *   (optional) Time zone identifier, as described at
-   *   http://php.net/manual/timezones.php Defaults to the time zone used to
-   *   display the page.
-   * @param string|null $langcode
-   *   (optional) Language code to translate to. NULL (default) means to use
-   *   the user interface language for the page.
-   *
-   * @return string
-   *   A translated date string in the requested format. Since the format may
-   *   contain user input, this value should be escaped when output.
+   * {@inheritdoc}
    */
   public function format($timestamp, $type = 'medium', $format = '', $timezone = NULL, $langcode = NULL) {
     if (!isset($timezone)) {
@@ -172,28 +145,7 @@ public function format($timestamp, $type = 'medium', $format = '', $timezone = N
   }
 
   /**
-   * Formats a time interval with the requested granularity.
-   *
-   * Note that for intervals over 30 days, the output is approximate: a "month"
-   * is always exactly 30 days, and a "year" is always 365 days. It is not
-   * possible to make a more exact representation, given that there is only one
-   * input in seconds. If you are formatting an interval between two specific
-   * timestamps, use \Drupal\Core\Datetime\DateFormatter::formatDiff() instead.
-   *
-   * @param int $interval
-   *   The length of the interval in seconds.
-   * @param int $granularity
-   *   (optional) How many different units to display in the string (2 by
-   *   default).
-   * @param string|null $langcode
-   *   (optional) langcode: The language code for the language used to format
-   *   the date. Defaults to NULL, which results in the user interface language
-   *   for the page being used.
-   *
-   * @return string
-   *   A translated string representation of the interval.
-   *
-   * @see \Drupal\Core\Datetime\DateFormatter::formatDiff()
+   * {@inheritdoc}
    */
   public function formatInterval($interval, $granularity = 2, $langcode = NULL) {
     $output = '';
@@ -218,21 +170,7 @@ public function formatInterval($interval, $granularity = 2, $langcode = NULL) {
   }
 
   /**
-   * Provides values for all date formatting characters for a given timestamp.
-   *
-   * @param string|null $langcode
-   *   (optional) Language code of the date format, if different from the site
-   *   default language.
-   * @param int|null $timestamp
-   *   (optional) The Unix timestamp to format, defaults to current time.
-   * @param string|null $timezone
-   *   (optional) The timezone to use, if different from the site's default
-   *   timezone.
-   *
-   * @return array
-   *   An array of formatted date values, indexed by the date format character.
-   *
-   * @see date()
+   * {@inheritdoc}
    */
   public function getSampleDateFormats($langcode = NULL, $timestamp = NULL, $timezone = NULL) {
     $timestamp = $timestamp ?: time();
@@ -245,30 +183,7 @@ public function getSampleDateFormats($langcode = NULL, $timestamp = NULL, $timez
   }
 
   /**
-   * Formats the time difference from the current request time to a timestamp.
-   *
-   * @param $timestamp
-   *   A UNIX timestamp to compare against the current request time.
-   * @param array $options
-   *   (optional) An associative array with additional options. The following
-   *   keys can be used:
-   *   - granularity: An integer value that signals how many different units to
-   *     display in the string. Defaults to 2.
-   *   - langcode: The language code for the language used to format the date.
-   *     Defaults to NULL, which results in the user interface language for the
-   *     page being used.
-   *   - strict: A Boolean value indicating whether or not the timestamp can be
-   *     before the current request time. If TRUE (default) and $timestamp is
-   *     before the current request time, the result string will be "0 seconds".
-   *     If FALSE and $timestamp is before the current request time, the result
-   *     string will be the formatted time difference.
-   *
-   * @return string
-   *   A translated string representation of the difference between the given
-   *   timestamp and the current request time. This interval is always positive.
-   *
-   * @see \Drupal\Core\Datetime\DateFormatter::formatDiff()
-   * @see \Drupal\Core\Datetime\DateFormatter::formatTimeDiffSince()
+   * {@inheritdoc}
    */
   public function formatTimeDiffUntil($timestamp, $options = array()) {
     $request_time = $this->requestStack->getCurrentRequest()->server->get('REQUEST_TIME');
@@ -276,30 +191,7 @@ public function formatTimeDiffUntil($timestamp, $options = array()) {
   }
 
   /**
-   * Formats the time difference from a timestamp to the current request time.
-   *
-   * @param $timestamp
-   *   A UNIX timestamp to compare against the current request time.
-   * @param array $options
-   *   (optional) An associative array with additional options. The following
-   *   keys can be used:
-   *   - granularity: An integer value that signals how many different units to
-   *     display in the string. Defaults to 2.
-   *   - langcode: The language code for the language used to format the date.
-   *     Defaults to NULL, which results in the user interface language for the
-   *     page being used.
-   *   - strict: A Boolean value indicating whether or not the timestamp can be
-   *     after the current request time. If TRUE (default) and $timestamp is
-   *     after the current request time, the result string will be "0 seconds".
-   *     If FALSE and $timestamp is after the current request time, the result
-   *     string will be the formatted time difference.
-   *
-   * @return string
-   *   A translated string representation of the difference between the given
-   *   timestamp and the current request time. This interval is always positive.
-   *
-   * @see \Drupal\Core\Datetime\DateFormatter::formatDiff()
-   * @see \Drupal\Core\Datetime\DateFormatter::formatTimeDiffUntil()
+   * {@inheritdoc}
    */
   public function formatTimeDiffSince($timestamp, $options = array()) {
     $request_time = $this->requestStack->getCurrentRequest()->server->get('REQUEST_TIME');
@@ -307,32 +199,7 @@ public function formatTimeDiffSince($timestamp, $options = array()) {
   }
 
   /**
-   * Formats a time interval between two timestamps.
-   *
-   * @param int $from
-   *   A UNIX timestamp, defining the from date and time.
-   * @param int $to
-   *   A UNIX timestamp, defining the to date and time.
-   * @param array $options
-   *   (optional) An associative array with additional options. The following
-   *   keys can be used:
-   *   - granularity: An integer value that signals how many different units to
-   *     display in the string. Defaults to 2.
-   *   - langcode: The language code for the language used to format the date.
-   *     Defaults to NULL, which results in the user interface language for the
-   *     page being used.
-   *   - strict: A Boolean value indicating whether or not the $from timestamp
-   *     can be after the $to timestamp. If TRUE (default) and $from is after
-   *     $to, the result string will be "0 seconds". If FALSE and $from is
-   *     after $to, the result string will be the formatted time difference.
-   *
-   * @return string
-   *   A translated string representation of the interval. This interval is
-   *   always positive.
-   *
-   * @see \Drupal\Core\Datetime\DateFormatter::formatInterval()
-   * @see \Drupal\Core\Datetime\DateFormatter::formatTimeDiffSince()
-   * @see \Drupal\Core\Datetime\DateFormatter::formatTimeDiffUntil()
+   * {@inheritdoc}
    */
   public function formatDiff($from, $to, $options = array()) {
 
diff --git a/core/lib/Drupal/Core/Datetime/DateFormatterInterface.php b/core/lib/Drupal/Core/Datetime/DateFormatterInterface.php
new file mode 100644
index 0000000..235e338
--- /dev/null
+++ b/core/lib/Drupal/Core/Datetime/DateFormatterInterface.php
@@ -0,0 +1,178 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Datetime\DateFormatterInterface.
+ */
+
+namespace Drupal\Core\Datetime;
+
+/**
+ * Provides an interface defining a date formatter.
+ */
+interface DateFormatterInterface {
+
+  /**
+   * Formats a date, using a date type or a custom date format string.
+   *
+   * @param int $timestamp
+   *   A UNIX timestamp to format.
+   * @param string $type
+   *   (optional) The format to use, one of:
+   *   - One of the built-in formats: 'short', 'medium',
+   *     'long', 'html_datetime', 'html_date', 'html_time',
+   *     'html_yearless_date', 'html_week', 'html_month', 'html_year'.
+   *   - The name of a date type defined by a date format config entity.
+   *   - The machine name of an administrator-defined date format.
+   *   - 'custom', to use $format.
+   *   Defaults to 'medium'.
+   * @param string $format
+   *   (optional) If $type is 'custom', a PHP date format string suitable for
+   *   input to date(). Use a backslash to escape ordinary text, so it does not
+   *   get interpreted as date format characters.
+   * @param string|null $timezone
+   *   (optional) Time zone identifier, as described at
+   *   http://php.net/manual/timezones.php Defaults to the time zone used to
+   *   display the page.
+   * @param string|null $langcode
+   *   (optional) Language code to translate to. NULL (default) means to use
+   *   the user interface language for the page.
+   *
+   * @return string
+   *   A translated date string in the requested format. Since the format may
+   *   contain user input, this value should be escaped when output.
+   */
+  public function format($timestamp, $type = 'medium', $format = '', $timezone = NULL, $langcode = NULL);
+
+  /**
+   * Formats a time interval with the requested granularity.
+   *
+   * Note that for intervals over 30 days, the output is approximate: a "month"
+   * is always exactly 30 days, and a "year" is always 365 days. It is not
+   * possible to make a more exact representation, given that there is only one
+   * input in seconds. If you are formatting an interval between two specific
+   * timestamps, use \Drupal\Core\Datetime\DateFormatter::formatDiff() instead.
+   *
+   * @param int $interval
+   *   The length of the interval in seconds.
+   * @param int $granularity
+   *   (optional) How many different units to display in the string (2 by
+   *   default).
+   * @param string|null $langcode
+   *   (optional) langcode: The language code for the language used to format
+   *   the date. Defaults to NULL, which results in the user interface language
+   *   for the page being used.
+   *
+   * @return string
+   *   A translated string representation of the interval.
+   *
+   * @see \Drupal\Core\Datetime\DateFormatter::formatDiff()
+   */
+  public function formatInterval($interval, $granularity = 2, $langcode = NULL);
+
+  /**
+   * Provides values for all date formatting characters for a given timestamp.
+   *
+   * @param string|null $langcode
+   *   (optional) Language code of the date format, if different from the site
+   *   default language.
+   * @param int|null $timestamp
+   *   (optional) The Unix timestamp to format, defaults to current time.
+   * @param string|null $timezone
+   *   (optional) The timezone to use, if different from the site's default
+   *   timezone.
+   *
+   * @return array
+   *   An array of formatted date values, indexed by the date format character.
+   *
+   * @see date()
+   */
+  public function getSampleDateFormats($langcode = NULL, $timestamp = NULL, $timezone = NULL);
+
+  /**
+   * Formats the time difference from the current request time to a timestamp.
+   *
+   * @param $timestamp
+   *   A UNIX timestamp to compare against the current request time.
+   * @param array $options
+   *   (optional) An associative array with additional options. The following
+   *   keys can be used:
+   *   - granularity: An integer value that signals how many different units to
+   *     display in the string. Defaults to 2.
+   *   - langcode: The language code for the language used to format the date.
+   *     Defaults to NULL, which results in the user interface language for the
+   *     page being used.
+   *   - strict: A Boolean value indicating whether or not the timestamp can be
+   *     before the current request time. If TRUE (default) and $timestamp is
+   *     before the current request time, the result string will be "0 seconds".
+   *     If FALSE and $timestamp is before the current request time, the result
+   *     string will be the formatted time difference.
+   *
+   * @return string
+   *   A translated string representation of the difference between the given
+   *   timestamp and the current request time. This interval is always positive.
+   *
+   * @see \Drupal\Core\Datetime\DateFormatter::formatDiff()
+   * @see \Drupal\Core\Datetime\DateFormatter::formatTimeDiffSince()
+   */
+  public function formatTimeDiffUntil($timestamp, $options = array());
+
+  /**
+   * Formats the time difference from a timestamp to the current request time.
+   *
+   * @param $timestamp
+   *   A UNIX timestamp to compare against the current request time.
+   * @param array $options
+   *   (optional) An associative array with additional options. The following
+   *   keys can be used:
+   *   - granularity: An integer value that signals how many different units to
+   *     display in the string. Defaults to 2.
+   *   - langcode: The language code for the language used to format the date.
+   *     Defaults to NULL, which results in the user interface language for the
+   *     page being used.
+   *   - strict: A Boolean value indicating whether or not the timestamp can be
+   *     after the current request time. If TRUE (default) and $timestamp is
+   *     after the current request time, the result string will be "0 seconds".
+   *     If FALSE and $timestamp is after the current request time, the result
+   *     string will be the formatted time difference.
+   *
+   * @return string
+   *   A translated string representation of the difference between the given
+   *   timestamp and the current request time. This interval is always positive.
+   *
+   * @see \Drupal\Core\Datetime\DateFormatter::formatDiff()
+   * @see \Drupal\Core\Datetime\DateFormatter::formatTimeDiffUntil()
+   */
+  public function formatTimeDiffSince($timestamp, $options = array());
+
+  /**
+   * Formats a time interval between two timestamps.
+   *
+   * @param int $from
+   *   A UNIX timestamp, defining the from date and time.
+   * @param int $to
+   *   A UNIX timestamp, defining the to date and time.
+   * @param array $options
+   *   (optional) An associative array with additional options. The following
+   *   keys can be used:
+   *   - granularity: An integer value that signals how many different units to
+   *     display in the string. Defaults to 2.
+   *   - langcode: The language code for the language used to format the date.
+   *     Defaults to NULL, which results in the user interface language for the
+   *     page being used.
+   *   - strict: A Boolean value indicating whether or not the $from timestamp
+   *     can be after the $to timestamp. If TRUE (default) and $from is after
+   *     $to, the result string will be "0 seconds". If FALSE and $from is
+   *     after $to, the result string will be the formatted time difference.
+   *
+   * @return string
+   *   A translated string representation of the interval. This interval is
+   *   always positive.
+   *
+   * @see \Drupal\Core\Datetime\DateFormatter::formatInterval()
+   * @see \Drupal\Core\Datetime\DateFormatter::formatTimeDiffSince()
+   * @see \Drupal\Core\Datetime\DateFormatter::formatTimeDiffUntil()
+   */
+  public function formatDiff($from, $to, $options = array());
+
+}
diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/TimestampAgoFormatter.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/TimestampAgoFormatter.php
index 6443669..b633d4d 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/TimestampAgoFormatter.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/TimestampAgoFormatter.php
@@ -8,7 +8,7 @@
 namespace Drupal\Core\Field\Plugin\Field\FieldFormatter;
 
 use Drupal\Component\Utility\SafeMarkup;
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Field\FieldDefinitionInterface;
 use Drupal\Core\Field\FieldItemListInterface;
 use Drupal\Core\Field\FormatterBase;
@@ -35,7 +35,7 @@ class TimestampAgoFormatter extends FormatterBase implements ContainerFactoryPlu
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -63,12 +63,12 @@ class TimestampAgoFormatter extends FormatterBase implements ContainerFactoryPlu
    *   The view mode.
    * @param array $third_party_settings
    *   Any third party settings.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    * @param \Symfony\Component\HttpFoundation\Request $request
    *   The current request.
    */
-  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, DateFormatter $date_formatter, Request $request) {
+  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, DateFormatterInterface $date_formatter, Request $request) {
     parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $label, $view_mode, $third_party_settings);
 
     $this->dateFormatter = $date_formatter;
diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/TimestampFormatter.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/TimestampFormatter.php
index 032e1d1..b6abbd5 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/TimestampFormatter.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/TimestampFormatter.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\Core\Field\Plugin\Field\FieldFormatter;
 
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Entity\EntityStorageInterface;
 use Drupal\Core\Field\FieldDefinitionInterface;
 use Drupal\Core\Field\FieldItemListInterface;
@@ -34,7 +34,7 @@ class TimestampFormatter extends FormatterBase implements ContainerFactoryPlugin
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -62,12 +62,12 @@ class TimestampFormatter extends FormatterBase implements ContainerFactoryPlugin
    *   The view mode.
    * @param array $third_party_settings
    *   Third party settings.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    * @param \Drupal\Core\Entity\EntityStorageInterface $date_format_storage
    *   The date format storage.
    */
-  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, DateFormatter $date_formatter, EntityStorageInterface $date_format_storage) {
+  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, DateFormatterInterface $date_formatter, EntityStorageInterface $date_format_storage) {
     parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $label, $view_mode, $third_party_settings);
 
     $this->dateFormatter = $date_formatter;
diff --git a/core/modules/aggregator/src/Controller/AggregatorController.php b/core/modules/aggregator/src/Controller/AggregatorController.php
index 54f4fbb..70c6697 100644
--- a/core/modules/aggregator/src/Controller/AggregatorController.php
+++ b/core/modules/aggregator/src/Controller/AggregatorController.php
@@ -9,7 +9,7 @@
 
 use Drupal\Component\Utility\Xss;
 use Drupal\Core\Controller\ControllerBase;
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\aggregator\FeedInterface;
 use Drupal\Core\Url;
 use Symfony\Component\HttpFoundation\Request;
@@ -24,17 +24,17 @@ class AggregatorController extends ControllerBase {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
   /**
    * Constructs a \Drupal\aggregator\Controller\AggregatorController object.
    *
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *    The date formatter service.
    */
-  public function __construct(DateFormatter $date_formatter) {
+  public function __construct(DateFormatterInterface $date_formatter) {
     $this->dateFormatter = $date_formatter;
   }
 
diff --git a/core/modules/aggregator/src/Plugin/aggregator/processor/DefaultProcessor.php b/core/modules/aggregator/src/Plugin/aggregator/processor/DefaultProcessor.php
index 0c98c67..21a67dd 100644
--- a/core/modules/aggregator/src/Plugin/aggregator/processor/DefaultProcessor.php
+++ b/core/modules/aggregator/src/Plugin/aggregator/processor/DefaultProcessor.php
@@ -14,7 +14,7 @@
 use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Database\Database;
 use Drupal\Core\Config\ConfigFactoryInterface;
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Entity\Query\QueryInterface;
 use Drupal\Core\Form\ConfigFormBaseTrait;
 use Drupal\Core\Form\FormStateInterface;
@@ -61,7 +61,7 @@ class DefaultProcessor extends AggregatorPluginSettingsBase implements Processor
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -80,10 +80,10 @@ class DefaultProcessor extends AggregatorPluginSettingsBase implements Processor
    *   The entity query object for feed items.
    * @param \Drupal\aggregator\ItemStorageInterface $item_storage
    *   The entity storage for feed items.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    */
-  public function __construct(array $configuration, $plugin_id, $plugin_definition, ConfigFactoryInterface $config, QueryInterface $item_query, ItemStorageInterface $item_storage, DateFormatter $date_formatter) {
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, ConfigFactoryInterface $config, QueryInterface $item_query, ItemStorageInterface $item_storage, DateFormatterInterface $date_formatter) {
     $this->configFactory = $config;
     $this->itemStorage = $item_storage;
     $this->itemQuery = $item_query;
diff --git a/core/modules/comment/src/Form/CommentAdminOverview.php b/core/modules/comment/src/Form/CommentAdminOverview.php
index 97515b2..df9b132 100644
--- a/core/modules/comment/src/Form/CommentAdminOverview.php
+++ b/core/modules/comment/src/Form/CommentAdminOverview.php
@@ -10,7 +10,7 @@
 use Drupal\comment\CommentInterface;
 use Drupal\comment\CommentStorageInterface;
 use Drupal\Component\Utility\Unicode;
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Entity\EntityManagerInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Form\FormBase;
@@ -39,7 +39,7 @@ class CommentAdminOverview extends FormBase {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -57,12 +57,12 @@ class CommentAdminOverview extends FormBase {
    *   The entity manager service.
    * @param \Drupal\comment\CommentStorageInterface $comment_storage
    *   The comment storage.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
    *   The module handler.
    */
-  public function __construct(EntityManagerInterface $entity_manager, CommentStorageInterface $comment_storage, DateFormatter $date_formatter, ModuleHandlerInterface $module_handler) {
+  public function __construct(EntityManagerInterface $entity_manager, CommentStorageInterface $comment_storage, DateFormatterInterface $date_formatter, ModuleHandlerInterface $module_handler) {
     $this->entityManager = $entity_manager;
     $this->commentStorage = $comment_storage;
     $this->dateFormatter = $date_formatter;
diff --git a/core/modules/config_translation/src/FormElement/DateFormat.php b/core/modules/config_translation/src/FormElement/DateFormat.php
index 637ebfe..6395a92 100644
--- a/core/modules/config_translation/src/FormElement/DateFormat.php
+++ b/core/modules/config_translation/src/FormElement/DateFormat.php
@@ -18,7 +18,7 @@ class DateFormat extends FormElementBase {
    * {@inheritdoc}
    */
   public function getTranslationElement(LanguageInterface $translation_language, $source_config, $translation_config) {
-    /** @var \Drupal\Core\Datetime\DateFormatter $date_formatter */
+    /** @var \Drupal\Core\Datetime\DateFormatterInterface $date_formatter */
     $date_formatter = \Drupal::service('date.formatter');
     $description = $this->t('A user-defined date format. See the <a href=":url">PHP manual</a> for available options.', array(':url' => 'http://php.net/manual/function.date.php'));
     $format = $this->t('Displayed as %date_format', array('%date_format' => $date_formatter->format(REQUEST_TIME, 'custom', $translation_config)));
diff --git a/core/modules/contact/src/MessageForm.php b/core/modules/contact/src/MessageForm.php
index 9cb5e54..fec2ca8 100644
--- a/core/modules/contact/src/MessageForm.php
+++ b/core/modules/contact/src/MessageForm.php
@@ -8,7 +8,7 @@
 namespace Drupal\contact;
 
 use Drupal\Component\Utility\SafeMarkup;
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Entity\ContentEntityForm;
 use Drupal\Core\Entity\EntityManagerInterface;
 use Drupal\Core\Flood\FloodInterface;
@@ -53,7 +53,7 @@ class MessageForm extends ContentEntityForm {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -68,10 +68,10 @@ class MessageForm extends ContentEntityForm {
    *   The language manager service.
    * @param \Drupal\contact\MailHandlerInterface $mail_handler
    *   The contact mail handler service.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date service.
    */
-  public function __construct(EntityManagerInterface $entity_manager, FloodInterface $flood, LanguageManagerInterface $language_manager, MailHandlerInterface $mail_handler, DateFormatter $date_formatter) {
+  public function __construct(EntityManagerInterface $entity_manager, FloodInterface $flood, LanguageManagerInterface $language_manager, MailHandlerInterface $mail_handler, DateFormatterInterface $date_formatter) {
     parent::__construct($entity_manager);
     $this->flood = $flood;
     $this->languageManager = $language_manager;
diff --git a/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeFormatterBase.php b/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeFormatterBase.php
index aad8c16..b146fbb 100644
--- a/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeFormatterBase.php
+++ b/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeFormatterBase.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\datetime\Plugin\Field\FieldFormatter;
 
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Datetime\DrupalDateTime;
 use Drupal\Core\Entity\EntityStorageInterface;
 use Drupal\Core\Field\FieldDefinitionInterface;
@@ -25,7 +25,7 @@
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -53,12 +53,12 @@
    *   The view mode.
    * @param array $third_party_settings
    *   Third party settings.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    * @param \Drupal\Core\Entity\EntityStorageInterface $date_format_storage
    *   The date format entity storage.
    */
-  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, DateFormatter $date_formatter, EntityStorageInterface $date_format_storage) {
+  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, DateFormatterInterface $date_formatter, EntityStorageInterface $date_format_storage) {
     parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $label, $view_mode, $third_party_settings);
 
     $this->dateFormatter = $date_formatter;
diff --git a/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeTimeAgoFormatter.php b/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeTimeAgoFormatter.php
index 0bc56c6..f6b85b0 100644
--- a/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeTimeAgoFormatter.php
+++ b/core/modules/datetime/src/Plugin/Field/FieldFormatter/DateTimeTimeAgoFormatter.php
@@ -8,7 +8,7 @@
 namespace Drupal\datetime\Plugin\Field\FieldFormatter;
 
 use Drupal\Component\Utility\SafeMarkup;
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Datetime\DrupalDateTime;
 use Drupal\Core\Field\FieldDefinitionInterface;
 use Drupal\Core\Field\FieldItemListInterface;
@@ -34,7 +34,7 @@ class DateTimeTimeAgoFormatter extends FormatterBase implements ContainerFactory
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -62,12 +62,12 @@ class DateTimeTimeAgoFormatter extends FormatterBase implements ContainerFactory
    *   The view mode.
    * @param array $third_party_settings
    *   Third party settings.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    * @param \Symfony\Component\HttpFoundation\Request $request
    *   The current request.
    */
-  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, DateFormatter $date_formatter, Request $request) {
+  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, DateFormatterInterface $date_formatter, Request $request) {
     parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $label, $view_mode, $third_party_settings);
 
     $this->dateFormatter = $date_formatter;
diff --git a/core/modules/datetime/src/Plugin/views/filter/Date.php b/core/modules/datetime/src/Plugin/views/filter/Date.php
index cc3caf7..e3553de 100644
--- a/core/modules/datetime/src/Plugin/views/filter/Date.php
+++ b/core/modules/datetime/src/Plugin/views/filter/Date.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\datetime\Plugin\views\filter;
 
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
 use Drupal\datetime\Plugin\Field\FieldType\DateTimeItem;
 use Drupal\views\FieldAPIHandlerTrait;
@@ -32,7 +32,7 @@ class Date extends NumericDate implements ContainerFactoryPluginInterface {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -61,12 +61,12 @@ class Date extends NumericDate implements ContainerFactoryPluginInterface {
    *   The plugin ID for the plugin instance.
    * @param mixed $plugin_definition
    *   The plugin implementation definition.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    * @param \Symfony\Component\HttpFoundation\RequestStack
    *   The request stack used to determine the current time.
    */
-  public function __construct(array $configuration, $plugin_id, $plugin_definition, DateFormatter $date_formatter, RequestStack $request_stack) {
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, DateFormatterInterface $date_formatter, RequestStack $request_stack) {
     parent::__construct($configuration, $plugin_id, $plugin_definition);
     $this->dateFormatter = $date_formatter;
     $this->requestStack = $request_stack;
diff --git a/core/modules/dblog/src/Controller/DbLogController.php b/core/modules/dblog/src/Controller/DbLogController.php
index eff6626..01d86ef 100644
--- a/core/modules/dblog/src/Controller/DbLogController.php
+++ b/core/modules/dblog/src/Controller/DbLogController.php
@@ -11,7 +11,7 @@
 use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Controller\ControllerBase;
 use Drupal\Core\Database\Connection;
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Form\FormBuilderInterface;
 use Drupal\Core\Logger\RfcLogLevel;
@@ -41,7 +41,7 @@ class DbLogController extends ControllerBase {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -78,12 +78,12 @@ public static function create(ContainerInterface $container) {
    *   A database connection.
    * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
    *   A module handler.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    * @param \Drupal\Core\Form\FormBuilderInterface $form_builder
    *   The form builder service.
    */
-  public function __construct(Connection $database, ModuleHandlerInterface $module_handler, DateFormatter $date_formatter, FormBuilderInterface $form_builder) {
+  public function __construct(Connection $database, ModuleHandlerInterface $module_handler, DateFormatterInterface $date_formatter, FormBuilderInterface $form_builder) {
     $this->database = $database;
     $this->moduleHandler = $module_handler;
     $this->dateFormatter = $date_formatter;
diff --git a/core/modules/node/src/Controller/NodeController.php b/core/modules/node/src/Controller/NodeController.php
index 299d253..c34062d 100644
--- a/core/modules/node/src/Controller/NodeController.php
+++ b/core/modules/node/src/Controller/NodeController.php
@@ -9,7 +9,7 @@
 
 use Drupal\Component\Utility\Xss;
 use Drupal\Core\Controller\ControllerBase;
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
 use Drupal\Core\Render\RendererInterface;
 use Drupal\Core\Url;
@@ -25,7 +25,7 @@ class NodeController extends ControllerBase implements ContainerInjectionInterfa
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -39,12 +39,12 @@ class NodeController extends ControllerBase implements ContainerInjectionInterfa
   /**
    * Constructs a NodeController object.
    *
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    * @param \Drupal\Core\Render\RendererInterface $renderer
    *   The renderer service.
    */
-  public function __construct(DateFormatter $date_formatter, RendererInterface $renderer) {
+  public function __construct(DateFormatterInterface $date_formatter, RendererInterface $renderer) {
     $this->dateFormatter = $date_formatter;
     $this->renderer = $renderer;
   }
diff --git a/core/modules/node/src/NodeListBuilder.php b/core/modules/node/src/NodeListBuilder.php
index 26f2876..35013f6 100644
--- a/core/modules/node/src/NodeListBuilder.php
+++ b/core/modules/node/src/NodeListBuilder.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\node;
 
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityListBuilder;
 use Drupal\Core\Entity\EntityStorageInterface;
@@ -26,7 +26,7 @@ class NodeListBuilder extends EntityListBuilder {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -44,12 +44,12 @@ class NodeListBuilder extends EntityListBuilder {
    *   The entity type definition.
    * @param \Drupal\Core\Entity\EntityStorageInterface $storage
    *   The entity storage class.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    * @param \Drupal\Core\Routing\RedirectDestinationInterface $redirect_destination
    *   The redirect destination service.
    */
-  public function __construct(EntityTypeInterface $entity_type, EntityStorageInterface $storage, DateFormatter $date_formatter, RedirectDestinationInterface $redirect_destination) {
+  public function __construct(EntityTypeInterface $entity_type, EntityStorageInterface $storage, DateFormatterInterface $date_formatter, RedirectDestinationInterface $redirect_destination) {
     parent::__construct($entity_type, $storage);
 
     $this->dateFormatter = $date_formatter;
diff --git a/core/modules/system/src/DateFormatListBuilder.php b/core/modules/system/src/DateFormatListBuilder.php
index 2f052d9..24a9ea0 100644
--- a/core/modules/system/src/DateFormatListBuilder.php
+++ b/core/modules/system/src/DateFormatListBuilder.php
@@ -8,7 +8,7 @@
 namespace Drupal\system;
 
 use Drupal\Core\Config\Entity\ConfigEntityListBuilder;
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityStorageInterface;
 use Drupal\Core\Entity\EntityTypeInterface;
@@ -24,7 +24,7 @@ class DateFormatListBuilder extends ConfigEntityListBuilder {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -35,10 +35,10 @@ class DateFormatListBuilder extends ConfigEntityListBuilder {
    *   The entity type definition.
    * @param \Drupal\Core\Entity\EntityStorageInterface $storage
    *   The entity storage class.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    */
-  public function __construct(EntityTypeInterface $entity_type, EntityStorageInterface $storage, DateFormatter $date_formatter) {
+  public function __construct(EntityTypeInterface $entity_type, EntityStorageInterface $storage, DateFormatterInterface $date_formatter) {
     parent::__construct($entity_type, $storage);
 
     $this->dateFormatter = $date_formatter;
diff --git a/core/modules/system/src/Form/CronForm.php b/core/modules/system/src/Form/CronForm.php
index e75c156..8d9545c 100644
--- a/core/modules/system/src/Form/CronForm.php
+++ b/core/modules/system/src/Form/CronForm.php
@@ -9,7 +9,7 @@
 
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\CronInterface;
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\State\StateInterface;
 use Drupal\Core\Form\ConfigFormBase;
@@ -38,7 +38,7 @@ class CronForm extends ConfigFormBase {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -51,10 +51,10 @@ class CronForm extends ConfigFormBase {
    *   The state key value store.
    * @param \Drupal\Core\CronInterface $cron
    *   The cron service.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    */
-  public function __construct(ConfigFactoryInterface $config_factory, StateInterface $state, CronInterface $cron, DateFormatter $date_formatter) {
+  public function __construct(ConfigFactoryInterface $config_factory, StateInterface $state, CronInterface $cron, DateFormatterInterface $date_formatter) {
     parent::__construct($config_factory);
     $this->state = $state;
     $this->cron = $cron;
diff --git a/core/modules/system/src/Form/DateFormatDeleteForm.php b/core/modules/system/src/Form/DateFormatDeleteForm.php
index 009700e..93d2141 100644
--- a/core/modules/system/src/Form/DateFormatDeleteForm.php
+++ b/core/modules/system/src/Form/DateFormatDeleteForm.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\system\Form;
 
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Entity\EntityDeleteForm;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -19,17 +19,17 @@ class DateFormatDeleteForm extends EntityDeleteForm {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
   /**
    * Constructs an DateFormatDeleteForm object.
    *
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    */
-  public function __construct(DateFormatter $date_formatter) {
+  public function __construct(DateFormatterInterface $date_formatter) {
     $this->dateFormatter = $date_formatter;
   }
 
diff --git a/core/modules/system/src/Form/DateFormatFormBase.php b/core/modules/system/src/Form/DateFormatFormBase.php
index 964ae96..252fba4 100644
--- a/core/modules/system/src/Form/DateFormatFormBase.php
+++ b/core/modules/system/src/Form/DateFormatFormBase.php
@@ -8,7 +8,7 @@
 namespace Drupal\system\Form;
 
 use Drupal\Core\Config\Entity\ConfigEntityStorageInterface;
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Language\LanguageInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -23,7 +23,7 @@
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -37,12 +37,12 @@
   /**
    * Constructs a new date format form.
    *
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date service.
    * @param \Drupal\Core\Config\Entity\ConfigEntityStorageInterface $date_format_storage
    *   The date format storage.
    */
-  public function __construct(DateFormatter $date_formatter, ConfigEntityStorageInterface $date_format_storage) {
+  public function __construct(DateFormatterInterface $date_formatter, ConfigEntityStorageInterface $date_format_storage) {
     $date = new DrupalDateTime();
 
     $this->dateFormatter = $date_formatter;
diff --git a/core/modules/system/src/Form/FileSystemForm.php b/core/modules/system/src/Form/FileSystemForm.php
index 002d7f7..7278c0c 100644
--- a/core/modules/system/src/Form/FileSystemForm.php
+++ b/core/modules/system/src/Form/FileSystemForm.php
@@ -8,7 +8,7 @@
 namespace Drupal\system\Form;
 
 use Drupal\Core\Config\ConfigFactoryInterface;
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\StreamWrapper\PrivateStream;
 use Drupal\Core\StreamWrapper\PublicStream;
@@ -25,7 +25,7 @@ class FileSystemForm extends ConfigFormBase {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -41,12 +41,12 @@ class FileSystemForm extends ConfigFormBase {
    *
    * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
    *   The factory for configuration objects.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    * @param \Drupal\Core\StreamWrapper\StreamWrapperManagerInterface $stream_wrapper_manager
    *   The stream wrapper manager.
    */
-  public function __construct(ConfigFactoryInterface $config_factory, DateFormatter $date_formatter, StreamWrapperManagerInterface $stream_wrapper_manager) {
+  public function __construct(ConfigFactoryInterface $config_factory, DateFormatterInterface $date_formatter, StreamWrapperManagerInterface $stream_wrapper_manager) {
     parent::__construct($config_factory);
     $this->dateFormatter = $date_formatter;
     $this->streamWrapperManager = $stream_wrapper_manager;
diff --git a/core/modules/system/src/Form/PerformanceForm.php b/core/modules/system/src/Form/PerformanceForm.php
index 4d28ac7..e6899dc 100644
--- a/core/modules/system/src/Form/PerformanceForm.php
+++ b/core/modules/system/src/Form/PerformanceForm.php
@@ -11,7 +11,7 @@
 use Drupal\Core\Form\ConfigFormBase;
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\Cache\CacheBackendInterface;
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -30,7 +30,7 @@ class PerformanceForm extends ConfigFormBase {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -54,14 +54,14 @@ class PerformanceForm extends ConfigFormBase {
    * @param \Drupal\Core\Config\ConfigFactoryInterface $config_factory
    *   The factory for configuration objects.
    * @param \Drupal\Core\Cache\CacheBackendInterface $render_cache
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    * @param \Drupal\Core\Asset\AssetCollectionOptimizerInterface $css_collection_optimizer
    *   The CSS asset collection optimizer service.
    * @param \Drupal\Core\Asset\AssetCollectionOptimizerInterface $js_collection_optimizer
    *   The JavaScript asset collection optimizer service.
    */
-  public function __construct(ConfigFactoryInterface $config_factory, CacheBackendInterface $render_cache, DateFormatter $date_formatter, AssetCollectionOptimizerInterface $css_collection_optimizer, AssetCollectionOptimizerInterface $js_collection_optimizer) {
+  public function __construct(ConfigFactoryInterface $config_factory, CacheBackendInterface $render_cache, DateFormatterInterface $date_formatter, AssetCollectionOptimizerInterface $css_collection_optimizer, AssetCollectionOptimizerInterface $js_collection_optimizer) {
     parent::__construct($config_factory);
 
     $this->renderCache = $render_cache;
diff --git a/core/modules/user/src/Controller/UserController.php b/core/modules/user/src/Controller/UserController.php
index 21c81a2..7897a91 100644
--- a/core/modules/user/src/Controller/UserController.php
+++ b/core/modules/user/src/Controller/UserController.php
@@ -9,7 +9,7 @@
 
 use Drupal\Component\Utility\Xss;
 use Drupal\Core\Controller\ControllerBase;
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\user\UserDataInterface;
 use Drupal\user\UserInterface;
 use Drupal\user\UserStorageInterface;
@@ -24,7 +24,7 @@ class UserController extends ControllerBase {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -45,14 +45,14 @@ class UserController extends ControllerBase {
   /**
    * Constructs a UserController object.
    *
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    * @param \Drupal\user\UserStorageInterface $user_storage
    *   The user storage.
    * @param \Drupal\user\UserDataInterface $user_data
    *   The user data service.
    */
-  public function __construct(DateFormatter $date_formatter, UserStorageInterface $user_storage, UserDataInterface $user_data) {
+  public function __construct(DateFormatterInterface $date_formatter, UserStorageInterface $user_storage, UserDataInterface $user_data) {
     $this->dateFormatter = $date_formatter;
     $this->userStorage = $user_storage;
     $this->userData = $user_data;
diff --git a/core/modules/user/src/UserListBuilder.php b/core/modules/user/src/UserListBuilder.php
index 85b52f2..a61ce89 100644
--- a/core/modules/user/src/UserListBuilder.php
+++ b/core/modules/user/src/UserListBuilder.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\user;
 
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityListBuilder;
 use Drupal\Core\Entity\EntityStorageInterface;
@@ -33,7 +33,7 @@ class UserListBuilder extends EntityListBuilder {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -53,12 +53,12 @@ class UserListBuilder extends EntityListBuilder {
    *   The entity storage class.
    * @param \Drupal\Core\Entity\Query\QueryFactory $query_factory
    *   The entity query factory.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    * @param \Drupal\Core\Routing\RedirectDestinationInterface $redirect_destination
    *   The redirect destination service.
    */
-  public function __construct(EntityTypeInterface $entity_type, EntityStorageInterface $storage, QueryFactory $query_factory, DateFormatter $date_formatter,  RedirectDestinationInterface $redirect_destination) {
+  public function __construct(EntityTypeInterface $entity_type, EntityStorageInterface $storage, QueryFactory $query_factory, DateFormatterInterface $date_formatter,  RedirectDestinationInterface $redirect_destination) {
     parent::__construct($entity_type, $storage);
     $this->queryFactory = $query_factory;
     $this->dateFormatter = $date_formatter;
diff --git a/core/modules/views/src/Plugin/views/cache/Time.php b/core/modules/views/src/Plugin/views/cache/Time.php
index d14ed1c..9ef1cd1e 100644
--- a/core/modules/views/src/Plugin/views/cache/Time.php
+++ b/core/modules/views/src/Plugin/views/cache/Time.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\views\Plugin\views\cache;
 
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Cache\Cache;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Drupal\Core\Form\FormStateInterface;
@@ -34,7 +34,7 @@ class Time extends CachePluginBase {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -54,12 +54,12 @@ class Time extends CachePluginBase {
    *   The plugin_id for the plugin instance.
    * @param mixed $plugin_definition
    *   The plugin implementation definition.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    * @param \Symfony\Component\HttpFoundation\Request $request
    *   The current request.
    */
-  public function __construct(array $configuration, $plugin_id, $plugin_definition, DateFormatter $date_formatter, Request $request) {
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, DateFormatterInterface $date_formatter, Request $request) {
     $this->dateFormatter = $date_formatter;
     $this->request = $request;
 
diff --git a/core/modules/views/src/Plugin/views/field/Date.php b/core/modules/views/src/Plugin/views/field/Date.php
index 340518c..517026f 100644
--- a/core/modules/views/src/Plugin/views/field/Date.php
+++ b/core/modules/views/src/Plugin/views/field/Date.php
@@ -11,7 +11,7 @@
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\views\ResultRow;
 use Symfony\Component\DependencyInjection\ContainerInterface;
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 
 /**
  * A handler to provide proper displays for dates.
@@ -25,7 +25,7 @@ class Date extends FieldPluginBase {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -45,12 +45,12 @@ class Date extends FieldPluginBase {
    *   The plugin ID for the plugin instance.
    * @param mixed $plugin_definition
    *   The plugin implementation definition.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    * @param \Drupal\Core\Entity\EntityStorageInterface $date_format_storage
    *   The date format storage.
    */
-  public function __construct(array $configuration, $plugin_id, $plugin_definition, DateFormatter $date_formatter, EntityStorageInterface $date_format_storage) {
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, DateFormatterInterface $date_formatter, EntityStorageInterface $date_format_storage) {
     parent::__construct($configuration, $plugin_id, $plugin_definition);
 
     $this->dateFormatter = $date_formatter;
diff --git a/core/modules/views/src/Plugin/views/field/TimeInterval.php b/core/modules/views/src/Plugin/views/field/TimeInterval.php
index 08ebef7..4c91421 100644
--- a/core/modules/views/src/Plugin/views/field/TimeInterval.php
+++ b/core/modules/views/src/Plugin/views/field/TimeInterval.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\views\Plugin\views\field;
 
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\views\ResultRow;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -24,7 +24,7 @@ class TimeInterval extends FieldPluginBase {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -37,10 +37,10 @@ class TimeInterval extends FieldPluginBase {
    *   The plugin_id for the plugin instance.
    * @param mixed $plugin_definition
    *   The plugin implementation definition.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date formatter service.
    */
-  public function __construct(array $configuration, $plugin_id, $plugin_definition, DateFormatter $date_formatter) {
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, DateFormatterInterface $date_formatter) {
     $this->dateFormatter = $date_formatter;
     parent::__construct($configuration, $plugin_id, $plugin_definition);
   }
diff --git a/core/modules/views_ui/src/ViewEditForm.php b/core/modules/views_ui/src/ViewEditForm.php
index 818984a..e225fd9 100644
--- a/core/modules/views_ui/src/ViewEditForm.php
+++ b/core/modules/views_ui/src/ViewEditForm.php
@@ -13,7 +13,7 @@
 use Drupal\Core\Ajax\AjaxResponse;
 use Drupal\Core\Ajax\HtmlCommand;
 use Drupal\Core\Ajax\ReplaceCommand;
-use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Datetime\DateFormatterInterface;
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Core\Form\FormStateInterface;
@@ -48,7 +48,7 @@ class ViewEditForm extends ViewFormBase {
   /**
    * The date formatter service.
    *
-   * @var \Drupal\Core\Datetime\DateFormatter
+   * @var \Drupal\Core\Datetime\DateFormatterInterface
    */
   protected $dateFormatter;
 
@@ -66,12 +66,12 @@ class ViewEditForm extends ViewFormBase {
    *   The factory for the temp store object.
    * @param \Symfony\Component\HttpFoundation\RequestStack $requestStack
    *   The request stack object.
-   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $date_formatter
    *   The date Formatter service.
    * @param \Drupal\Core\Render\ElementInfoManagerInterface $element_info
    *   The element info manager.
    */
-  public function __construct(SharedTempStoreFactory $temp_store_factory, RequestStack $requestStack, DateFormatter $date_formatter, ElementInfoManagerInterface $element_info) {
+  public function __construct(SharedTempStoreFactory $temp_store_factory, RequestStack $requestStack, DateFormatterInterface $date_formatter, ElementInfoManagerInterface $element_info) {
     $this->tempStore = $temp_store_factory->get('views');
     $this->requestStack = $requestStack;
     $this->dateFormatter = $date_formatter;