Naked Objects - Building a title from multiple fields

Naked Objects
By Richard Pawson and Robert Matthews

Enriching object behaviours

Building a title from multiple fields

All org.nakedobjects.object.Naked objects have a title that can be used when presenting the object to the user. These titles are generated by the title method, which returns a org.nakedobjects.object.Title object containing a textual title.

For value objects this is a formatted version of the value, for example "10:50 am" or "₤3.50". For business objects this is some form of identifier.

If a business objects has a field that uniquely identifies each instance, such as an invoice number, then the title method can simply get the Title object from that identifying field. The following method from the City class passes on the title held by the name value object for that city.

public Title title() {
    return name.title();
}

In other cases a business object's title will be derived from multiple attributes. The Title object provides a set of useful constructors and methods that assist in creating titles from String objects, other naked objects (usually those held within an object's own fields), and other Title objects. For example, for the Customer class, we may want to create the title from the customer's first and last names. A Title object can append various objects to itself and in true overloaded style will convert numbers, strings and other naked objects to strings before appending them, and look after all the spacing for you. Consider the following method:

public Title title() {
    Title title = firstName.title();
    Title fullTitle = title.append(lastName);
    return fullTitle;
}

Assuming that the value held by firstName is 'Robert' and lastName is 'Matthews' then the call to append will result in the title being 'Robert Matthews'. If, however, firstName is empty then the title will correctly be 'Matthews' (with no leading space). Similarly if lastName is empty then the result will be 'Robert' with no trailing space.

Simple String objects can also be appended for additional formatting. Changing the above example to:

public Title title() {
		 Title title = lastName.title();
		 Title fullTitle = title.append(",", firstName);
		 return fullTitle;
}

changes the ordering of the names and produces the correct three variations: 'Matthews, Robert', 'Matthews' and 'Robert'. The joining string is additional to the delimiting space.

(If you do not require spaces between the elements of a title, use the concat method instead of append.)

One other useful thing to remember is that each of these methods returns the object it was called upon. This allows the append and concat methods to be chained, shortening your title method even further. This is the terse version of the previous code:

public Title title() {
    return lastName.title().append(",", lastName);
}

Remember, too, that reference variables for other business objects aren't guaranteed to refer to anything (they could be null) and could also be unresolved (they don't contain the required information). For this reason it is important not to use a reference variable directly, and to check that a reference is not null before using it. This is another reason why you should use the field's get... method even for internal operations. You can then use the returned reference (null or otherwise) as a parameter to one of the Title constructors or methods. This way the title class will check the reference and if it is null will deal with it in a suitable fashion without throwing a NullPointerException.

The Title methods that take the String default value as their last parameter will display this value when the reference passed is null. The following example shows this. This method will work whether or not the Order field has a value, and whether or not the Order object's data has been loaded yet.

public Title title() {
    return new Title(getOrder(), "New Order");
}