import java.util.Scanner; // I use scanner because it's command line.

public class Login {
public void run() {
    Scanner scan = new Scanner (new File("the\\dir\\myFile.extension"));
    Scanner keyboard = new Scanner (System.in);
    String user = scan.nextLine();
    String pass = scan.nextLine(); // looks at selected file in scan

    String inpUser = keyboard.nextLine();
    String inpPass = keyboard.nextLine(); // gets input from user

    if (inpUser.equals(user) && inpPass.equals(pass)) {
        System.out.print("your login message");
    } else {
        System.out.print("your error message");
    }
}
}