diff --git a/src/Symfony/Component/EventDispatcher/Debug/TraceableEventDispatcher.php b/src/Symfony/Component/EventDispatcher/Debug/TraceableEventDispatcher.php
index ea946419ca15d..edea60f866f98 100644
--- a/src/Symfony/Component/EventDispatcher/Debug/TraceableEventDispatcher.php
+++ b/src/Symfony/Component/EventDispatcher/Debug/TraceableEventDispatcher.php
@@ -32,20 +32,18 @@ class TraceableEventDispatcher implements EventDispatcherInterface, ResetInterfa
     protected $logger;
     protected $stopwatch;
 
-    private $callStack;
-    private $dispatcher;
-    private $wrappedListeners;
-    private $orphanedEvents;
-    private $requestStack;
-    private $currentRequestHash = '';
+    private ?\SplObjectStorage $callStack = null;
+    private EventDispatcherInterface $dispatcher;
+    private array $wrappedListeners = [];
+    private array $orphanedEvents = [];
+    private ?RequestStack $requestStack;
+    private string $currentRequestHash = '';
 
     public function __construct(EventDispatcherInterface $dispatcher, Stopwatch $stopwatch, LoggerInterface $logger = null, RequestStack $requestStack = null)
     {
         $this->dispatcher = $dispatcher;
         $this->stopwatch = $stopwatch;
         $this->logger = $logger;
-        $this->wrappedListeners = [];
-        $this->orphanedEvents = [];
         $this->requestStack = $requestStack;
     }
 
diff --git a/src/Symfony/Component/EventDispatcher/Debug/WrappedListener.php b/src/Symfony/Component/EventDispatcher/Debug/WrappedListener.php
index 7a2cd6920e797..7df21922aa38e 100644
--- a/src/Symfony/Component/EventDispatcher/Debug/WrappedListener.php
+++ b/src/Symfony/Component/EventDispatcher/Debug/WrappedListener.php
@@ -21,17 +21,17 @@
  */
 final class WrappedListener
 {
-    private $listener;
-    private $optimizedListener;
-    private $name;
-    private $called;
-    private $stoppedPropagation;
-    private $stopwatch;
-    private $dispatcher;
-    private $pretty;
-    private $stub;
-    private $priority;
-    private static $hasClassStub;
+    private string|array|object $listener;
+    private ?\Closure $optimizedListener;
+    private string $name;
+    private bool $called = false;
+    private bool $stoppedPropagation = false;
+    private Stopwatch $stopwatch;
+    private ?EventDispatcherInterface $dispatcher;
+    private string $pretty;
+    private ClassStub|string $stub;
+    private ?int $priority = null;
+    private static bool $hasClassStub;
 
     public function __construct(callable|array $listener, ?string $name, Stopwatch $stopwatch, EventDispatcherInterface $dispatcher = null)
     {
@@ -39,8 +39,6 @@ public function __construct(callable|array $listener, ?string $name, Stopwatch $
         $this->optimizedListener = $listener instanceof \Closure ? $listener : (\is_callable($listener) ? \Closure::fromCallable($listener) : null);
         $this->stopwatch = $stopwatch;
         $this->dispatcher = $dispatcher;
-        $this->called = false;
-        $this->stoppedPropagation = false;
 
         if (\is_array($listener)) {
             $this->name = \is_object($listener[0]) ? get_debug_type($listener[0]) : $listener[0];
@@ -66,12 +64,10 @@ public function __construct(callable|array $listener, ?string $name, Stopwatch $
             $this->name = $name;
         }
 
-        if (null === self::$hasClassStub) {
-            self::$hasClassStub = class_exists(ClassStub::class);
-        }
+        self::$hasClassStub ??= class_exists(ClassStub::class);
     }
 
-    public function getWrappedListener()
+    public function getWrappedListener(): callable|array
     {
         return $this->listener;
     }
@@ -93,9 +89,7 @@ public function getPretty(): string
 
     public function getInfo(string $eventName): array
     {
-        if (null === $this->stub) {
-            $this->stub = self::$hasClassStub ? new ClassStub($this->pretty.'()', $this->listener) : $this->pretty.'()';
-        }
+        $this->stub ??= self::$hasClassStub ? new ClassStub($this->pretty.'()', $this->listener) : $this->pretty.'()';
 
         return [
             'event' => $eventName,
diff --git a/src/Symfony/Component/EventDispatcher/DependencyInjection/AddEventAliasesPass.php b/src/Symfony/Component/EventDispatcher/DependencyInjection/AddEventAliasesPass.php
index b77811b38b17c..13b4336aa4eeb 100644
--- a/src/Symfony/Component/EventDispatcher/DependencyInjection/AddEventAliasesPass.php
+++ b/src/Symfony/Component/EventDispatcher/DependencyInjection/AddEventAliasesPass.php
@@ -21,7 +21,7 @@
  */
 class AddEventAliasesPass implements CompilerPassInterface
 {
-    private $eventAliases;
+    private array $eventAliases;
 
     public function __construct(array $eventAliases)
     {
diff --git a/src/Symfony/Component/EventDispatcher/DependencyInjection/RegisterListenersPass.php b/src/Symfony/Component/EventDispatcher/DependencyInjection/RegisterListenersPass.php
index 352737572d1dc..cc481321c9abc 100644
--- a/src/Symfony/Component/EventDispatcher/DependencyInjection/RegisterListenersPass.php
+++ b/src/Symfony/Component/EventDispatcher/DependencyInjection/RegisterListenersPass.php
@@ -25,10 +25,10 @@
  */
 class RegisterListenersPass implements CompilerPassInterface
 {
-    private $hotPathEvents = [];
-    private $hotPathTagName = 'container.hot_path';
-    private $noPreloadEvents = [];
-    private $noPreloadTagName = 'container.no_preload';
+    private array $hotPathEvents = [];
+    private string $hotPathTagName = 'container.hot_path';
+    private array $noPreloadEvents = [];
+    private string $noPreloadTagName = 'container.no_preload';
 
     /**
      * @return $this
diff --git a/src/Symfony/Component/EventDispatcher/EventDispatcher.php b/src/Symfony/Component/EventDispatcher/EventDispatcher.php
index 638c3f4830afe..021d668eaa004 100644
--- a/src/Symfony/Component/EventDispatcher/EventDispatcher.php
+++ b/src/Symfony/Component/EventDispatcher/EventDispatcher.php
@@ -31,9 +31,9 @@
  */
 class EventDispatcher implements EventDispatcherInterface
 {
-    private $listeners = [];
-    private $sorted = [];
-    private $optimized;
+    private array $listeners = [];
+    private array $sorted = [];
+    private array $optimized;
 
     public function __construct()
     {
@@ -49,7 +49,7 @@ public function dispatch(object $event, string $eventName = null): object
     {
         $eventName = $eventName ?? \get_class($event);
 
-        if (null !== $this->optimized) {
+        if (isset($this->optimized)) {
             $listeners = $this->optimized[$eventName] ?? (empty($this->listeners[$eventName]) ? [] : $this->optimizeListeners($eventName));
         } else {
             $listeners = $this->getListeners($eventName);
diff --git a/src/Symfony/Component/EventDispatcher/ImmutableEventDispatcher.php b/src/Symfony/Component/EventDispatcher/ImmutableEventDispatcher.php
index fd04ff76f90fa..6bc8bfffaeb96 100644
--- a/src/Symfony/Component/EventDispatcher/ImmutableEventDispatcher.php
+++ b/src/Symfony/Component/EventDispatcher/ImmutableEventDispatcher.php
@@ -18,7 +18,7 @@
  */
 class ImmutableEventDispatcher implements EventDispatcherInterface
 {
-    private $dispatcher;
+    private EventDispatcherInterface $dispatcher;
 
     public function __construct(EventDispatcherInterface $dispatcher)
     {