Core/InternalModule.php
public function checkPhpFileExists($sClassName)
    {
        if ($this->isMetadataVersionGreaterEqual('2.0')) {
            $composerClassLoader = $this->getModuleHelper()->getAutoloader();

            return $composerClassLoader->findFile($sClassName);
        } else {
            $sExtensionPath = $sClassName . '.php';
            $res = $this->checkFileExists($sExtensionPath);
            return $res;
        }
    }
public function checkPhpFileExists($sClassName)
    {
        if ($this->isMetadataVersionGreaterEqual('2.0')) {
            $composerClassLoader = $this->getModuleHelper()->getAutoloader();

            return $composerClassLoader->findFile($sClassName);
        } else {
            $sExtensionPath = $sClassName . '.php';
            $res = $this->checkFileExists($sExtensionPath);
            return $res;
        }
    }
checks if module file exists on directory
switches between metadata version for checking
checks also for namespace class if metadata version = 2.0

@param string $sClassName
@param string $sExtention

@return bool