public class Account
{
    public string UserName { get; private set; }
    public string Password { get; private set; }

    public Account(string UserName, string Password)
    {
        this.UserName = UserName;
        this.Password = Password;
    }
}

// main method in some other class
public static Main(){
    Account account = new Account ("someUserName", "somePassword");

    Console.Writeln("my user name : " + account.UserName);
    Console.Writeln("my password  : " + account.Password);

    // But the following is not valid :
    account.UserName = "someNewValue";
    account.Password = "someOtherPassword";
}