UserDB.php

<?php

interface DBConnectionInterface {
    public function connect();
}

class MySQLConnection implements DBConnectionInterface {
  
    public function connect() {
        // Return the MySQL connection...
    }
}

class UserDB {
  
    private $dbConnection;
    
    public function __construct(DBConnectionInterface $dbConnection) {
        $this->dbConnection = $dbConnection;
    }
  
    public function store(User $user) {
        // Store the user into a database...
    }
}

I think on line 18 it will be
public function __construct(MySQLConnection $dbConnection) {

I think on line 18 it will be
public function __construct(MySQLConnection $dbConnection) {

No, because an entity should depend on abstractions and not on concretions.

@Idenela I think on line 19 , $this->$dbConnection = $dbConnection; this should change to $this->dbConnection = $dbConnection;

@Vijaysinh Updated! Thank you!