API design involving standard and custom settings

Question

Suppose a class allows some kind of configuration that has some well-known default values but also has the option of defining a custom value. For example, suppose you want to let users configure a person's title. They can choose from a set of standard values (Mr., Mrs., Ms., etc.) but they can also specify a custom (Dr.). What is the most elegant way to put this in an API? Some examples in Java:

public class Person {
  public enum Title {MR, MRS, MS, CUSTOM};

  setTitle(Title title, String customTitle);
}

This one is quite bad because whenever you specify anything else than Title.CUSTOM the second argument is silently ignored.

So maybe:

public class Person {
  public enum Title { MR, MRS, MS, CUSTOM};

  setTitle(Title title);
  setCustomTitle(String title);
}

I don't really like this one either, because it's not immediately clear that calling one will overwrite the effects of the other method. Is there a more elegant interface that I'm overlooking?

Answer 1

You could overload the setTitle mthod

public class Person{
    public enum Title { MR, MRS, MS, CUSTOM };
    private Title EnumTitle
    private String CustomTitle;

    public void setTitle(Title title); //Does what you'd expect
    public void setTitle(String title)
    {
        EnumTitle = Title.CUSTOM;
        CustomTitle = title;
    }

    /**
     * This does present some problems when returning the value, however.
     *
     * My first thought to solve this problem is to always expect the 
     * output of getTitle() to be a string - either the custom title or
     * a string representation of the enum value.
     */ 
}

Answer 2

Is there a reason why you need the title enumeration or is this just an implementation detail?

Depending what you want to do with the api this could be a simple solution.

public class Person {
  public static final String MR = "MR";
  public static final String MRS = "MRS";
  public static final String MS= "MS";

  public void setCustomTitle(String title);
}

Maybe it is a good idea to distinguish title from sex if this is necessary for your processing

  public enum Sex { Female, Male, };
  public void setSex(Sex sex); //Does what you'd expect