I can't connect MySQL using MySQLConnector (Communications link failure )

Question

I'm learning about Java JDBC and I want to connect with MySQL. I've added a connection driver, updated JDK and MySQL to the newest versions, set up MySQL online, but I still get an error about a Communications link failure. Here is my code:

package jdbcConnection;

import java.sql.*;

public class ConnectionTest {
    public static void main(String[] args) {
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost::3306/tree","root","pass");
            Statement stmt = con.createStatement();
            System.out.println("Inserting records");
            String sql = "Insert into fruit values(43)";
            stmt.executeUpdate(sql);
            con.close();
        }
        catch(Exception e) {
            System.out.println(e);
        }
    }
}

This is the error:

com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.