Question

Given

public enum Title {

MR("Mr."), MRS("Mrs."), MS("Ms.");

private final String title;

private Title(String t) {
    title = t;
}

public String format(String last, String first) {
    return title + "" + first + "" + last;
}
}

public static void main(String[] args){
    System.out.println(Title.MR.format("Doe","John"));
}

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Does anyone know how to explain this ? Keep in mind the code is not fully complete. This happens to be a question from a book. The Answer to this question is Mr. John Doe.

Thanks

Answer 1

Well, first of all, consider reading this, in order to understand what is an Enum, how it works, and when you should use it.

Now, concerning your Enum example, you are declaring an Enumerated type with three possible values: MR, MRS, and MS. Enums, just like Classes, can have methods and constructors. In your example, Title has a single argument constructor — which stores a description of the Title –, and a method that basically prepends the description to a given name — the format method.

So, when you invoke Title.MR.format("Doe","John")), first you get an instance of the MR Title, and then you invoke the format method, which returns Mr.John Doe.

Also note that only one instance of each Title is created, so that invoking Title.MR several times will always return the same objet.