diff --git a/lib/private/AppFramework/DependencyInjection/DIContainer.php b/lib/private/AppFramework/DependencyInjection/DIContainer.php
index 439404f26ce6a..e994959a6ff4f 100644
--- a/lib/private/AppFramework/DependencyInjection/DIContainer.php
+++ b/lib/private/AppFramework/DependencyInjection/DIContainer.php
@@ -67,13 +67,14 @@
 use OCP\RichObjectStrings\IValidator;
 use OCP\Encryption\IManager;
 use OCA\WorkflowEngine\Manager;
+use OC\CapabilitiesManager;
 
 class DIContainer extends SimpleContainer implements IAppContainer {
 
 	/**
 	 * @var array
 	 */
-	private $middleWares = array();
+	private $middleWares = [];
 
 	/** @var ServerContainer */
 	private $server;
@@ -84,7 +85,7 @@ class DIContainer extends SimpleContainer implements IAppContainer {
 	 * @param array $urlParams
 	 * @param ServerContainer|null $server
 	 */
-	public function __construct($appName, $urlParams = array(), ServerContainer $server = null){
+	public function __construct($appName, $urlParams = [], ServerContainer $server = null){
 		parent::__construct();
 		$this['AppName'] = $appName;
 		$this['urlParams'] = $urlParams;
@@ -104,7 +105,7 @@ public function __construct($appName, $urlParams = array(), ServerContainer $ser
 		/**
 		 * Core services
 		 */
-		$this->registerService(IOutput::class, function($c){
+		$this->registerService(IOutput::class, function(){
 			return new Output($this->getServer()->getWebRoot());
 		});
 
@@ -138,7 +139,7 @@ public function __construct($appName, $urlParams = array(), ServerContainer $ser
 
 		$this->registerAlias(\OC\User\Session::class, \OCP\IUserSession::class);
 
-		$this->registerService(IServerContainer::class, function ($c) {
+		$this->registerService(IServerContainer::class, function () {
 			return $this->getServer();
 		});
 		$this->registerAlias('ServerContainer', IServerContainer::class);
@@ -166,7 +167,7 @@ public function __construct($appName, $urlParams = array(), ServerContainer $ser
 			return $c->getServer()->getThemingDefaults();
 		});
 
-		$this->registerService(IManager::class, function ($c) {
+		$this->registerService(IManager::class, function () {
 			return $this->getServer()->getEncryptionManager();
 		});
 
@@ -178,7 +179,7 @@ public function __construct($appName, $urlParams = array(), ServerContainer $ser
 			return $c->query(Validator::class);
 		});
 
-		$this->registerService(\OC\Security\IdentityProof\Manager::class, function ($c) {
+		$this->registerService(\OC\Security\IdentityProof\Manager::class, function () {
 			return new \OC\Security\IdentityProof\Manager(
 				$this->getServer()->query(\OC\Files\AppData\Factory::class),
 				$this->getServer()->getCrypto(),
@@ -339,16 +340,14 @@ public function __construct($appName, $urlParams = array(), ServerContainer $ser
 	/**
 	 * @return \OCP\IServerContainer
 	 */
-	public function getServer()
-	{
+	public function getServer(): IServerContainer {
 		return $this->server;
 	}
 
 	/**
 	 * @param string $middleWare
-	 * @return boolean|null
 	 */
-	public function registerMiddleWare($middleWare) {
+	public function registerMiddleWare(string $middleWare) {
 		$this->middleWares[] = $middleWare;
 	}
 
@@ -356,7 +355,7 @@ public function registerMiddleWare($middleWare) {
 	 * used to return the appname of the set application
 	 * @return string the name of your application
 	 */
-	public function getAppName() {
+	public function getAppName(): string {
 		return $this->query('AppName');
 	}
 
@@ -364,7 +363,7 @@ public function getAppName() {
 	 * @deprecated use IUserSession->isLoggedIn()
 	 * @return boolean
 	 */
-	public function isLoggedIn() {
+	public function isLoggedIn(): bool {
 		return \OC::$server->getUserSession()->isLoggedIn();
 	}
 
@@ -372,7 +371,7 @@ public function isLoggedIn() {
 	 * @deprecated use IGroupManager->isAdmin($userId)
 	 * @return boolean
 	 */
-	public function isAdminUser() {
+	public function isAdminUser(): bool {
 		$uid = $this->getUserId();
 		return \OC_User::isAdminUser($uid);
 	}
@@ -413,8 +412,8 @@ public function log($message, $level) {
 	 *
 	 * @param string $serviceName e.g. 'OCA\Files\Capabilities'
 	 */
-	public function registerCapability($serviceName) {
-		$this->query('OC\CapabilitiesManager')->registerCapability(function() use ($serviceName) {
+	public function registerCapability(string $serviceName) {
+		$this->query(CapabilitiesManager::class)->registerCapability(function() use ($serviceName) {
 			return $this->query($serviceName);
 		});
 	}
@@ -424,7 +423,7 @@ public function registerCapability($serviceName) {
 	 * @return mixed
 	 * @throws QueryException if the query could not be resolved
 	 */
-	public function query($name) {
+	public function query(string $name) {
 		try {
 			return $this->queryNoFallback($name);
 		} catch (QueryException $firstException) {
@@ -444,7 +443,7 @@ public function query($name) {
 	 * @return mixed
 	 * @throws QueryException if the query could not be resolved
 	 */
-	public function queryNoFallback($name) {
+	public function queryNoFallback(string $name) {
 		$name = $this->sanitizeName($name);
 
 		if ($this->offsetExists($name)) {
diff --git a/lib/private/AppFramework/Utility/SimpleContainer.php b/lib/private/AppFramework/Utility/SimpleContainer.php
index 47a6f95f747c7..3e30d01c6fc4a 100644
--- a/lib/private/AppFramework/Utility/SimpleContainer.php
+++ b/lib/private/AppFramework/Utility/SimpleContainer.php
@@ -1,4 +1,5 @@
 <?php
+declare(strict_types=1);
 /**
  * @copyright Copyright (c) 2016, ownCloud, Inc.
  *
@@ -90,7 +91,7 @@ private function buildClass(ReflectionClass $class) {
 	 * @return \stdClass
 	 * @throws QueryException if the class could not be found or instantiated
 	 */
-	public function resolve($name) {
+	public function resolve(string $name) {
 		$baseMsg = 'Could not resolve ' . $name . '!';
 		try {
 			$class = new ReflectionClass($name);
@@ -111,7 +112,7 @@ public function resolve($name) {
 	 * @return mixed registered service for the given $name
 	 * @throws QueryException if the query could not be resolved
 	 */
-	public function query($name) {
+	public function query(string $name) {
 		$name = $this->sanitizeName($name);
 		if ($this->offsetExists($name)) {
 			return $this->offsetGet($name);
@@ -128,7 +129,7 @@ public function query($name) {
 	 * @param string $name
 	 * @param mixed $value
 	 */
-	public function registerParameter($name, $value) {
+	public function registerParameter(string $name, $value) {
 		$this[$name] = $value;
 	}
 
@@ -141,7 +142,7 @@ public function registerParameter($name, $value) {
 	 * @param Closure $closure the closure to be called on service creation
 	 * @param bool $shared
 	 */
-	public function registerService($name, Closure $closure, $shared = true) {
+	public function registerService(string $name, Closure $closure, bool $shared = true) {
 		$name = $this->sanitizeName($name);
 		if (isset($this[$name]))  {
 			unset($this[$name]);
@@ -160,17 +161,17 @@ public function registerService($name, Closure $closure, $shared = true) {
 	 * @param string $alias the alias that should be registered
 	 * @param string $target the target that should be resolved instead
 	 */
-	public function registerAlias($alias, $target) {
+	public function registerAlias(string $alias, string $target) {
 		$this->registerService($alias, function (IContainer $container) use ($target) {
 			return $container->query($target);
 		}, false);
 	}
 
-	/*
+	/**
 	 * @param string $name
 	 * @return string
 	 */
-	protected function sanitizeName($name) {
+	protected function sanitizeName(string $name): string {
 		if (isset($name[0]) && $name[0] === '\\') {
 			return ltrim($name, '\\');
 		}
diff --git a/lib/private/ServerContainer.php b/lib/private/ServerContainer.php
index 40e261df4d699..e6526d814c201 100644
--- a/lib/private/ServerContainer.php
+++ b/lib/private/ServerContainer.php
@@ -1,4 +1,5 @@
 <?php
+declare(strict_types=1);
 /**
  * @copyright Copyright (c) 2016, ownCloud, Inc.
  *
@@ -57,7 +58,7 @@ public function __construct() {
 	 * @param string $appName
 	 * @param string $appNamespace
 	 */
-	public function registerNamespace($appName, $appNamespace) {
+	public function registerNamespace(string $appName, string $appNamespace) {
 		// Cut of OCA\ and lowercase
 		$appNamespace = strtolower(substr($appNamespace, strrpos($appNamespace, '\\') + 1));
 		$this->namespaces[$appNamespace] = $appName;
@@ -67,7 +68,7 @@ public function registerNamespace($appName, $appNamespace) {
 	 * @param string $appName
 	 * @param DIContainer $container
 	 */
-	public function registerAppContainer($appName, DIContainer $container) {
+	public function registerAppContainer(string $appName, DIContainer $container) {
 		$this->appContainers[strtolower(App::buildAppNamespace($appName, ''))] = $container;
 	}
 
@@ -77,7 +78,7 @@ public function registerAppContainer($appName, DIContainer $container) {
 	 * @return DIContainer
 	 * @throws QueryException
 	 */
-	protected function getAppContainer($namespace, $sensitiveNamespace) {
+	protected function getAppContainer(string $namespace, string $sensitiveNamespace): DIContainer {
 		if (isset($this->appContainers[$namespace])) {
 			return $this->appContainers[$namespace];
 		}
@@ -104,7 +105,7 @@ protected function getAppContainer($namespace, $sensitiveNamespace) {
 	 * @return mixed registered service for the given $name
 	 * @throws QueryException if the query could not be resolved
 	 */
-	public function query($name) {
+	public function query(string $name) {
 		$name = $this->sanitizeName($name);
 
 		// In case the service starts with OCA\ we try to find the service in
diff --git a/lib/public/AppFramework/IAppContainer.php b/lib/public/AppFramework/IAppContainer.php
index 2fa0bcdd5aa0d..dd1aa8629807f 100644
--- a/lib/public/AppFramework/IAppContainer.php
+++ b/lib/public/AppFramework/IAppContainer.php
@@ -27,6 +27,7 @@
 namespace OCP\AppFramework;
 
 use OCP\IContainer;
+use OCP\IServerContainer;
 
 /**
  * Class IAppContainer
@@ -42,20 +43,19 @@ interface IAppContainer extends IContainer {
 	 * @return string the name of your application
 	 * @since 6.0.0
 	 */
-	public function getAppName();
+	public function getAppName(): string;
 
 	/**
 	 * @return \OCP\IServerContainer
 	 * @since 6.0.0
 	 */
-	public function getServer();
+	public function getServer(): IServerContainer;
 
 	/**
 	 * @param string $middleWare
-	 * @return boolean
 	 * @since 6.0.0
 	 */
-	public function registerMiddleWare($middleWare);
+	public function registerMiddleWare(string $middleWare);
 
 	/**
 	 * Register a capability
@@ -63,5 +63,5 @@ public function registerMiddleWare($middleWare);
 	 * @param string $serviceName e.g. 'OCA\Files\Capabilities'
 	 * @since 8.2.0
 	 */
-	 public function registerCapability($serviceName);
+	 public function registerCapability(string $serviceName);
 }
diff --git a/lib/public/IContainer.php b/lib/public/IContainer.php
index f7ca0697671c3..dd1e9a8b40264 100644
--- a/lib/public/IContainer.php
+++ b/lib/public/IContainer.php
@@ -1,4 +1,5 @@
 <?php
+declare(strict_types=1);
 /**
  * @copyright Copyright (c) 2016, ownCloud, Inc.
  *
@@ -55,7 +56,7 @@ interface IContainer {
 	 * @since 8.2.0
 	 * @throws QueryException if the class could not be found or instantiated
 	 */
-	public function resolve($name);
+	public function resolve(string $name);
 
 	/**
 	 * Look up a service for a given name in the container.
@@ -65,7 +66,7 @@ public function resolve($name);
 	 * @throws QueryException if the query could not be resolved
 	 * @since 6.0.0
 	 */
-	public function query($name);
+	public function query(string $name);
 
 	/**
 	 * A value is stored in the container with it's corresponding name
@@ -75,7 +76,7 @@ public function query($name);
 	 * @return void
 	 * @since 6.0.0
 	 */
-	public function registerParameter($name, $value);
+	public function registerParameter(string $name, $value);
 
 	/**
 	 * A service is registered in the container where a closure is passed in which will actually
@@ -90,7 +91,7 @@ public function registerParameter($name, $value);
 	 * @return void
 	 * @since 6.0.0
 	 */
-	public function registerService($name, Closure $closure, $shared = true);
+	public function registerService(string $name, Closure $closure, bool $shared = true);
 
 	/**
 	 * Shortcut for returning a service from a service under a different key,
@@ -100,5 +101,5 @@ public function registerService($name, Closure $closure, $shared = true);
 	 * @param string $target the target that should be resolved instead
 	 * @since 8.2.0
 	 */
-	public function registerAlias($alias, $target);
+	public function registerAlias(string $alias, string $target);
 }