Dependency Injection

public class AccountsSettingsService : IAccountsSettingsService

  {

    private readonly MultisiteProviderFactory multisiteProviderFactory;

    public const string PageNotFoundUrl = "/404";

//instead of setter/getter

    public static AccountsSettingsService Instance => new AccountsSettingsService();

//default constructor that automatically instantiates a MultisiteProviderFactory

    public AccountsSettingsService() : this(new MultisiteProviderFactory()) { }

//constructor that instantiates it as well but with a passed instance

    public AccountsSettingsService(MultisiteProviderFactory multisiteProvideFactory)

    {

      this.multisiteProviderFactory = multisiteProvideFactory;

    }

}