diff --git a/src/Symfony/Component/Config/ConfigCacheFactory.php b/src/Symfony/Component/Config/ConfigCacheFactory.php
index bfb70cb2ceda5..bcec95c11d9c1 100644
--- a/src/Symfony/Component/Config/ConfigCacheFactory.php
+++ b/src/Symfony/Component/Config/ConfigCacheFactory.php
@@ -35,7 +35,7 @@ public function __construct(bool $debug)
     /**
      * {@inheritdoc}
      */
-    public function cache($file, $callback)
+    public function cache(string $file, $callback)
     {
         if (!\is_callable($callback)) {
             throw new \InvalidArgumentException(sprintf('Invalid type for callback argument. Expected callable, but got "%s".', \gettype($callback)));
diff --git a/src/Symfony/Component/Config/ConfigCacheFactoryInterface.php b/src/Symfony/Component/Config/ConfigCacheFactoryInterface.php
index 8e80142b7816d..255b85a6575a7 100644
--- a/src/Symfony/Component/Config/ConfigCacheFactoryInterface.php
+++ b/src/Symfony/Component/Config/ConfigCacheFactoryInterface.php
@@ -28,5 +28,5 @@ interface ConfigCacheFactoryInterface
      *
      * @return ConfigCacheInterface The cache instance
      */
-    public function cache($file, $callable);
+    public function cache(string $file, $callable);
 }
diff --git a/src/Symfony/Component/Config/ConfigCacheInterface.php b/src/Symfony/Component/Config/ConfigCacheInterface.php
index 7c47ad70a5685..001e7e7c105e8 100644
--- a/src/Symfony/Component/Config/ConfigCacheInterface.php
+++ b/src/Symfony/Component/Config/ConfigCacheInterface.php
@@ -45,5 +45,5 @@ public function isFresh();
      *
      * @throws \RuntimeException When the cache file cannot be written
      */
-    public function write($content, array $metadata = null);
+    public function write(string $content, array $metadata = null);
 }
diff --git a/src/Symfony/Component/Config/Definition/ArrayNode.php b/src/Symfony/Component/Config/Definition/ArrayNode.php
index 43697ef27943c..9fabdd5628a4c 100644
--- a/src/Symfony/Component/Config/Definition/ArrayNode.php
+++ b/src/Symfony/Component/Config/Definition/ArrayNode.php
@@ -102,40 +102,32 @@ public function getXmlRemappings()
     /**
      * Sets whether to add default values for this array if it has not been
      * defined in any of the configuration files.
-     *
-     * @param bool $boolean
      */
-    public function setAddIfNotSet($boolean)
+    public function setAddIfNotSet(bool $boolean)
     {
-        $this->addIfNotSet = (bool) $boolean;
+        $this->addIfNotSet = $boolean;
     }
 
     /**
      * Sets whether false is allowed as value indicating that the array should be unset.
-     *
-     * @param bool $allow
      */
-    public function setAllowFalse($allow)
+    public function setAllowFalse(bool $allow)
     {
-        $this->allowFalse = (bool) $allow;
+        $this->allowFalse = $allow;
     }
 
     /**
      * Sets whether new keys can be defined in subsequent configurations.
-     *
-     * @param bool $allow
      */
-    public function setAllowNewKeys($allow)
+    public function setAllowNewKeys(bool $allow)
     {
-        $this->allowNewKeys = (bool) $allow;
+        $this->allowNewKeys = $allow;
     }
 
     /**
      * Sets if deep merging should occur.
-     *
-     * @param bool $boolean
      */
-    public function setPerformDeepMerging($boolean)
+    public function setPerformDeepMerging(bool $boolean)
     {
         $this->performDeepMerging = (bool) $boolean;
     }
@@ -146,16 +138,16 @@ public function setPerformDeepMerging($boolean)
      * @param bool $boolean To allow extra keys
      * @param bool $remove  To remove extra keys
      */
-    public function setIgnoreExtraKeys($boolean, $remove = true)
+    public function setIgnoreExtraKeys(bool $boolean, $remove = true)
     {
-        $this->ignoreExtraKeys = (bool) $boolean;
+        $this->ignoreExtraKeys = $boolean;
         $this->removeExtraKeys = $this->ignoreExtraKeys && $remove;
     }
 
     /**
      * {@inheritdoc}
      */
-    public function setName($name)
+    public function setName(string $name)
     {
         $this->name = $name;
     }
diff --git a/src/Symfony/Component/Config/Definition/PrototypeNodeInterface.php b/src/Symfony/Component/Config/Definition/PrototypeNodeInterface.php
index 8bbb84d4dcc7b..53ed43667ffce 100644
--- a/src/Symfony/Component/Config/Definition/PrototypeNodeInterface.php
+++ b/src/Symfony/Component/Config/Definition/PrototypeNodeInterface.php
@@ -23,5 +23,5 @@ interface PrototypeNodeInterface extends NodeInterface
      *
      * @param string $name The name of the node
      */
-    public function setName($name);
+    public function setName(string $name);
 }
diff --git a/src/Symfony/Component/Config/Definition/VariableNode.php b/src/Symfony/Component/Config/Definition/VariableNode.php
index 0bcb28f233b17..fd193d8e73418 100644
--- a/src/Symfony/Component/Config/Definition/VariableNode.php
+++ b/src/Symfony/Component/Config/Definition/VariableNode.php
@@ -56,15 +56,15 @@ public function getDefaultValue()
      *
      * @param bool $boolean True if this entity will accept empty values
      */
-    public function setAllowEmptyValue($boolean)
+    public function setAllowEmptyValue(bool $boolean)
     {
-        $this->allowEmptyValue = (bool) $boolean;
+        $this->allowEmptyValue = $boolean;
     }
 
     /**
      * {@inheritdoc}
      */
-    public function setName($name)
+    public function setName(string $name)
     {
         $this->name = $name;
     }
diff --git a/src/Symfony/Component/Config/FileLocator.php b/src/Symfony/Component/Config/FileLocator.php
index b80026ea0769b..345e63e6cd61e 100644
--- a/src/Symfony/Component/Config/FileLocator.php
+++ b/src/Symfony/Component/Config/FileLocator.php
@@ -33,7 +33,7 @@ public function __construct($paths = [])
     /**
      * {@inheritdoc}
      */
-    public function locate($name, $currentPath = null, $first = true)
+    public function locate(string $name, string $currentPath = null, $first = true)
     {
         if ('' == $name) {
             throw new \InvalidArgumentException('An empty file name is not valid to be located.');
@@ -81,7 +81,7 @@ public function locate($name, $currentPath = null, $first = true)
      *
      * @return bool
      */
-    private function isAbsolutePath($file)
+    private function isAbsolutePath(string $file)
     {
         if ('/' === $file[0] || '\\' === $file[0]
             || (\strlen($file) > 3 && ctype_alpha($file[0])
diff --git a/src/Symfony/Component/Config/FileLocatorInterface.php b/src/Symfony/Component/Config/FileLocatorInterface.php
index cf3c2e594df85..e3ca1d49c4066 100644
--- a/src/Symfony/Component/Config/FileLocatorInterface.php
+++ b/src/Symfony/Component/Config/FileLocatorInterface.php
@@ -30,5 +30,5 @@ interface FileLocatorInterface
      * @throws \InvalidArgumentException        If $name is empty
      * @throws FileLocatorFileNotFoundException If a file is not found
      */
-    public function locate($name, $currentPath = null, $first = true);
+    public function locate(string $name, string $currentPath = null, bool $first = true);
 }
diff --git a/src/Symfony/Component/Config/Loader/DelegatingLoader.php b/src/Symfony/Component/Config/Loader/DelegatingLoader.php
index e40e57d7af6aa..2ec64cb021246 100644
--- a/src/Symfony/Component/Config/Loader/DelegatingLoader.php
+++ b/src/Symfony/Component/Config/Loader/DelegatingLoader.php
@@ -31,7 +31,7 @@ public function __construct(LoaderResolverInterface $resolver)
     /**
      * {@inheritdoc}
      */
-    public function load($resource, $type = null)
+    public function load($resource, string $type = null)
     {
         if (false === $loader = $this->resolver->resolve($resource, $type)) {
             throw new LoaderLoadException($resource, null, null, null, $type);
@@ -43,7 +43,7 @@ public function load($resource, $type = null)
     /**
      * {@inheritdoc}
      */
-    public function supports($resource, $type = null)
+    public function supports($resource, string $type = null)
     {
         return false !== $this->resolver->resolve($resource, $type);
     }
diff --git a/src/Symfony/Component/Config/Loader/GlobFileLoader.php b/src/Symfony/Component/Config/Loader/GlobFileLoader.php
index f432b45ba4fe8..fecb1c5d073ac 100644
--- a/src/Symfony/Component/Config/Loader/GlobFileLoader.php
+++ b/src/Symfony/Component/Config/Loader/GlobFileLoader.php
@@ -21,7 +21,7 @@ class GlobFileLoader extends FileLoader
     /**
      * {@inheritdoc}
      */
-    public function load($resource, $type = null)
+    public function load($resource, string $type = null)
     {
         return $this->import($resource);
     }
@@ -29,7 +29,7 @@ public function load($resource, $type = null)
     /**
      * {@inheritdoc}
      */
-    public function supports($resource, $type = null)
+    public function supports($resource, string $type = null)
     {
         return 'glob' === $type;
     }
diff --git a/src/Symfony/Component/Config/Loader/LoaderInterface.php b/src/Symfony/Component/Config/Loader/LoaderInterface.php
index dfca9dd27bf0d..4dfb42c53fada 100644
--- a/src/Symfony/Component/Config/Loader/LoaderInterface.php
+++ b/src/Symfony/Component/Config/Loader/LoaderInterface.php
@@ -21,22 +21,20 @@ interface LoaderInterface
     /**
      * Loads a resource.
      *
-     * @param mixed       $resource The resource
-     * @param string|null $type     The resource type or null if unknown
+     * @param mixed $resource The resource
      *
      * @throws \Exception If something went wrong
      */
-    public function load($resource, $type = null);
+    public function load($resource, string $type = null);
 
     /**
      * Returns whether this class supports the given resource.
      *
-     * @param mixed       $resource A resource
-     * @param string|null $type     The resource type or null if unknown
+     * @param mixed $resource A resource
      *
      * @return bool True if this class supports the given resource, false otherwise
      */
-    public function supports($resource, $type = null);
+    public function supports($resource, string $type = null);
 
     /**
      * Gets the loader resolver.
diff --git a/src/Symfony/Component/Config/Loader/LoaderResolver.php b/src/Symfony/Component/Config/Loader/LoaderResolver.php
index c99efda4fd365..d243b91d42542 100644
--- a/src/Symfony/Component/Config/Loader/LoaderResolver.php
+++ b/src/Symfony/Component/Config/Loader/LoaderResolver.php
@@ -39,7 +39,7 @@ public function __construct(array $loaders = [])
     /**
      * {@inheritdoc}
      */
-    public function resolve($resource, $type = null)
+    public function resolve($resource, string $type = null)
     {
         foreach ($this->loaders as $loader) {
             if ($loader->supports($resource, $type)) {
diff --git a/src/Symfony/Component/Config/Loader/LoaderResolverInterface.php b/src/Symfony/Component/Config/Loader/LoaderResolverInterface.php
index 40f1a1a63f295..2c45a4cbd79b7 100644
--- a/src/Symfony/Component/Config/Loader/LoaderResolverInterface.php
+++ b/src/Symfony/Component/Config/Loader/LoaderResolverInterface.php
@@ -26,5 +26,5 @@ interface LoaderResolverInterface
      *
      * @return LoaderInterface|false The loader or false if none is able to load the resource
      */
-    public function resolve($resource, $type = null);
+    public function resolve($resource, string $type = null);
 }
diff --git a/src/Symfony/Component/Config/Resource/SelfCheckingResourceChecker.php b/src/Symfony/Component/Config/Resource/SelfCheckingResourceChecker.php
index d72203bc1a42c..eab332393ab28 100644
--- a/src/Symfony/Component/Config/Resource/SelfCheckingResourceChecker.php
+++ b/src/Symfony/Component/Config/Resource/SelfCheckingResourceChecker.php
@@ -28,7 +28,7 @@ public function supports(ResourceInterface $metadata)
         return $metadata instanceof SelfCheckingResourceInterface;
     }
 
-    public function isFresh(ResourceInterface $resource, $timestamp)
+    public function isFresh(ResourceInterface $resource, int $timestamp)
     {
         /* @var SelfCheckingResourceInterface $resource */
         return $resource->isFresh($timestamp);
diff --git a/src/Symfony/Component/Config/ResourceCheckerConfigCache.php b/src/Symfony/Component/Config/ResourceCheckerConfigCache.php
index 34dc35d5f51f8..39a16db9513fd 100644
--- a/src/Symfony/Component/Config/ResourceCheckerConfigCache.php
+++ b/src/Symfony/Component/Config/ResourceCheckerConfigCache.php
@@ -116,7 +116,7 @@ public function isFresh()
      *
      * @throws \RuntimeException When cache file can't be written
      */
-    public function write($content, array $metadata = null)
+    public function write(string $content, array $metadata = null)
     {
         $mode = 0666;
         $umask = umask();
diff --git a/src/Symfony/Component/Config/ResourceCheckerConfigCacheFactory.php b/src/Symfony/Component/Config/ResourceCheckerConfigCacheFactory.php
index 0338635ff5a62..fc1702f3cb89a 100644
--- a/src/Symfony/Component/Config/ResourceCheckerConfigCacheFactory.php
+++ b/src/Symfony/Component/Config/ResourceCheckerConfigCacheFactory.php
@@ -32,7 +32,7 @@ public function __construct(iterable $resourceCheckers = [])
     /**
      * {@inheritdoc}
      */
-    public function cache($file, $callback)
+    public function cache(string $file, $callback)
     {
         if (!\is_callable($callback)) {
             throw new \InvalidArgumentException(sprintf('Invalid type for callback argument. Expected callable, but got "%s".', \gettype($callback)));
diff --git a/src/Symfony/Component/Config/ResourceCheckerInterface.php b/src/Symfony/Component/Config/ResourceCheckerInterface.php
index 612d77786446a..f9724442dd562 100644
--- a/src/Symfony/Component/Config/ResourceCheckerInterface.php
+++ b/src/Symfony/Component/Config/ResourceCheckerInterface.php
@@ -44,5 +44,5 @@ public function supports(ResourceInterface $metadata);
      *
      * @return bool True if the resource has not changed since the given timestamp, false otherwise
      */
-    public function isFresh(ResourceInterface $resource, $timestamp);
+    public function isFresh(ResourceInterface $resource, int $timestamp);
 }
diff --git a/src/Symfony/Component/Config/Tests/FileLocatorTest.php b/src/Symfony/Component/Config/Tests/FileLocatorTest.php
index 0bd97f7d8a38e..d4299111cf111 100644
--- a/src/Symfony/Component/Config/Tests/FileLocatorTest.php
+++ b/src/Symfony/Component/Config/Tests/FileLocatorTest.php
@@ -115,6 +115,6 @@ public function testLocateEmpty()
     {
         $loader = new FileLocator([__DIR__.'/Fixtures']);
 
-        $loader->locate(null, __DIR__);
+        $loader->locate('', __DIR__);
     }
 }