Call to undefined method error when using Singleton in PHP

I have a project where I use aws sd开发者_StackOverflow中文版k for php. Here I am trying to create S3Client with singleton. But it does not create S3Client outside of the constructor.

Here is the class:

class ClientController
{

private static $client;

private function __construct()
{
    try {
        self::$client = new S3Client([
            'region' => AWS_S3_REGION,
            'version' => AWS_S3_VERSION,
            'credentials' => [
                'key' => AWS_S3_KEY,
                'secret' => AWS_S3_SECRET_KEY
            ],
        ]);
        echo 'test3333333333';
    } catch (Exception $ex) {
        echo $ex->getMessage();
        //logging
    }
}

public static function s3Client()
{
    if(!isset(self::$client)) {
        echo 'test1';
        self::$client = new ClientController();
    }
    echo 'test2';
    return self::$client;
}

}

And index file I run in another folder:

var_dump(ClientController::s3Client()->getObject(array(
    'Bucket' => 'jetdeneme',
    'Key' => $request,
)));

Output:

test1test3333333333test2
Fatal error: Uncaught Error: Call to undefined method ClientController::getObject() in C:\xampp\htdocs\cdn\index.php:10

When I use the above var_dump in ClientController's constructor, it doesn't give an error. But it gives outside of the constructor. I just want to create and use the Client using the static function.