diff --git a/rector.php b/rector.php
index 6070321..1cb8628 100644
--- a/rector.php
+++ b/rector.php
@@ -25,7 +25,7 @@
         SetList::CODE_QUALITY,
         SetList::CODING_STYLE,
         //SetList::NAMING,
-        //SetList::TYPE_DECLARATION,
+        SetList::TYPE_DECLARATION,
         //SetList::PRIVATIZATION,
         //SetList::EARLY_RETURN,
         //SetList::TYPE_DECLARATION,
diff --git a/src/CodeClone.php b/src/CodeClone.php
index 4d4461a..61b6cd4 100644
--- a/src/CodeClone.php
+++ b/src/CodeClone.php
@@ -63,7 +63,7 @@ public function lines(string $indent = ''): string
             $this->lines = implode(
                 '',
                 array_map(
-                    static function (string $line) use ($indent) {
+                    static function (string $line) use ($indent): string {
                         return $indent.$line;
                     },
                     \array_slice(
diff --git a/src/Detector/Strategy/SuffixTree/ApproximateCloneDetectingSuffixTree.php b/src/Detector/Strategy/SuffixTree/ApproximateCloneDetectingSuffixTree.php
index 82f5f92..a552bee 100644
--- a/src/Detector/Strategy/SuffixTree/ApproximateCloneDetectingSuffixTree.php
+++ b/src/Detector/Strategy/SuffixTree/ApproximateCloneDetectingSuffixTree.php
@@ -37,43 +37,37 @@ class ApproximateCloneDetectingSuffixTree extends SuffixTree
      *
      * @var int[]
      */
-    private $leafCount = [];
+    private array $leafCount = [];
 
     /**
      * This is the distance between two entries in the {@link #cloneInfos} map.
-     *
-     * @var int
      */
-    private $INDEX_SPREAD = 10;
+    private int $INDEX_SPREAD = 10;
 
     /**
      * This map stores for each position the relevant clone infos.
      *
      * @var array<CloneInfo[]>
      */
-    private $cloneInfos = [];
+    private array $cloneInfos = [];
 
     /**
      * The maximal length of a clone. This influences the size of the
      * (quadratic) {@link #edBuffer}.
-     *
-     * @var int
      */
-    private $MAX_LENGTH = 1024;
+    private int $MAX_LENGTH = 1024;
 
     /**
      * Buffer used for calculating edit distance.
      *
      * @var array<int[]>
      */
-    private $edBuffer = [];
+    private array $edBuffer = [];
 
     /**
      * Number of units that must be equal at the start of a clone.
-     *
-     * @var int
      */
-    private $headEquality = 10;
+    private int $headEquality = 10;
 
     /**
      * Create a new suffix tree from a given word. The word given as parameter
diff --git a/src/Detector/Strategy/SuffixTree/CloneInfo.php b/src/Detector/Strategy/SuffixTree/CloneInfo.php
index 05507d2..e9ffbc9 100644
--- a/src/Detector/Strategy/SuffixTree/CloneInfo.php
+++ b/src/Detector/Strategy/SuffixTree/CloneInfo.php
@@ -44,10 +44,8 @@ class CloneInfo
 
     /**
      * Number of occurrences of the clone.
-     *
-     * @var int
      */
-    private $occurrences;
+    private int $occurrences;
 
     /** Constructor. */
     public function __construct(int $length, int $position, int $occurrences, AbstractToken $token, PairList $otherClones)
diff --git a/src/Detector/Strategy/SuffixTree/PairList.php b/src/Detector/Strategy/SuffixTree/PairList.php
index cf0bdc2..196c317 100644
--- a/src/Detector/Strategy/SuffixTree/PairList.php
+++ b/src/Detector/Strategy/SuffixTree/PairList.php
@@ -31,24 +31,22 @@ class PairList
 {
     /**
      * The current size.
-     *
-     * @var int
      */
-    private $size = 0;
+    private int $size = 0;
 
     /**
      * The array used for storing the S.
      *
      * @var S[]
      */
-    private $firstElements;
+    private array $firstElements;
 
     /**
      * The array used for storing the T.
      *
      * @var T[]
      */
-    private $secondElements;
+    private array $secondElements;
 
     public function __construct(int $initialCapacity)
     {
diff --git a/src/Detector/Strategy/SuffixTree/Sentinel.php b/src/Detector/Strategy/SuffixTree/Sentinel.php
index f679551..ac29fa6 100644
--- a/src/Detector/Strategy/SuffixTree/Sentinel.php
+++ b/src/Detector/Strategy/SuffixTree/Sentinel.php
@@ -22,7 +22,7 @@
 class Sentinel extends AbstractToken
 {
     /** @var int The hash value used. */
-    private $hash;
+    private int $hash;
 
     public function __construct()
     {
diff --git a/src/Detector/Strategy/SuffixTree/SuffixTree.php b/src/Detector/Strategy/SuffixTree/SuffixTree.php
index 728690c..68dd45b 100644
--- a/src/Detector/Strategy/SuffixTree/SuffixTree.php
+++ b/src/Detector/Strategy/SuffixTree/SuffixTree.php
@@ -47,10 +47,8 @@ class SuffixTree
 {
     /**
      * Infinity in this context.
-     *
-     * @var int
      */
-    protected $INFTY;
+    protected int $INFTY;
 
     /**
      * The word we are working on.
@@ -91,10 +89,8 @@ class SuffixTree
     /**
      * The next node function realized as a hash table. This corresponds to the
      * <em>g</em> function used in Ukkonen's paper.
-     *
-     * @var SuffixTreeHashTable
      */
-    protected $nextNode;
+    protected \SebastianBergmann\PHPCPD\Detector\Strategy\SuffixTree\SuffixTreeHashTable $nextNode;
 
     /**
      * An array giving for each node the index where the first child will be
@@ -130,19 +126,15 @@ class SuffixTree
     /**
      * The node we are currently at as a "global" variable (as it is always
      * passed unchanged). This is called <i>s</i> in Ukkonen's paper.
-     *
-     * @var int
      */
-    private $currentNode = 0;
+    private int $currentNode = 0;
 
     /**
      * Beginning of the word part of the reference pair. This is kept "global"
      * (in constrast to the end) as this is passed unchanged to all functions.
      * Ukkonen calls this <em>k</em>.
-     *
-     * @var int
      */
-    private $refWordBegin = 0;
+    private int $refWordBegin = 0;
 
     /**
      * This is the new (or old) explicit state as returned by
diff --git a/src/Detector/Strategy/SuffixTree/SuffixTreeHashTable.php b/src/Detector/Strategy/SuffixTree/SuffixTreeHashTable.php
index 98eedfc..cc732ce 100644
--- a/src/Detector/Strategy/SuffixTree/SuffixTreeHashTable.php
+++ b/src/Detector/Strategy/SuffixTree/SuffixTreeHashTable.php
@@ -37,7 +37,7 @@ class SuffixTreeHashTable
      *
      * @var int[]
      */
-    private $allowedSizes = [53, 97, 193, 389, 769, 1543,
+    private array $allowedSizes = [53, 97, 193, 389, 769, 1543,
         3079, 6151, 12289, 24593, 49157, 98317, 196613, 393241, 786433,
         1572869, 3145739, 6291469, 12582917, 25165843, 50331653, 100663319,
         201326611, 402653189, 805306457, 1610612741, ];
@@ -54,42 +54,36 @@ class SuffixTreeHashTable
      *
      * @var int[]
      */
-    private $keyNodes;
+    private array $keyNodes;
 
     /**
      * Storage space for the character part of the key.
      *
      * @var array<AbstractToken|null>
      */
-    private $keyChars;
+    private array $keyChars;
 
     /**
      * Storage space for the result node.
      *
      * @var int[]
      */
-    private $resultNodes;
+    private array $resultNodes;
 
     /**
      * Debug info: number of stored nodes.
-     *
-     * @var int
      */
-    private $_numStoredNodes = 0;
+    private int $_numStoredNodes = 0;
 
     /**
      * Debug info: number of calls to find so far.
-     *
-     * @var int
      */
-    private $_numFind = 0;
+    private int $_numFind = 0;
 
     /**
      * Debug info: number of collisions (i.e. wrong finds) during find so far.
-     *
-     * @var int
      */
-    private $_numColl = 0;
+    private int $_numColl = 0;
 
     /**
      * Creates a new hash table for the given number of nodes. Trying to add