<?php

final class DemoFile
{
    public function run(string $var): bool
    {
        $checkRes = self::check($var);
        
        return $checkRes;
    }
    
    private static function check($value): bool
    {
        return true;
    }
}

public function run(string $var): bool
     {
-        $checkRes = self::check($var);
+        $checkRes = $this->check();
         
         return $checkRes;
     }
     
-    private static function check($value): bool
+    private function check($value): bool
     {
         return true;
     }

public function run(string $var): bool
     {
-        $checkRes = self::check($var);
+        $checkRes = $this->check($var);
         
         return $checkRes;
     }
     
-    private static function check($value): bool
+    private function check($value): bool
     {
         return true;
     }