Solutions - Design Patterns Java - page 319

Builder (Chapter 15)
SOLUTION 15.1
The point of making the Reservation constructor protected is that it limits the ability to
instantiate your class. You want to compel other developers to create Reservation objects
with a builder rather than with the Reservation constructor. You could make
the constructor package protected, which would ensure that only other classes within your
package can construct Reservation objects. Making the constructor protected leaves
open the possibility of subclassing Reservation from another package. Note that making
the constructor's visibility private would break the builder classes' ability to instantiate
the Reservation class.
SOLUTION 15.2
The build() method of UnforgivingBuilder throws an exception if any attribute is
invalid and otherwise returns a valid Reservation object. Here is one implementation:
public Reservation build() throws BuilderException
{
if (date == null)
{
throw new BuilderException("Valid date not found");
}
if (city == null)
{
throw new BuilderException("Valid city not found");
}
if (headcount < MINHEAD)
{
throw new BuilderException(
"Minimum headcount is " + MINHEAD);
}
if (dollarsPerHead * headcount < MINTOTAL)
{
throw new BuilderException(
"Minimum total cost is " + MINTOTAL);
}
return new Reservation(
date,
headcount,
city,
dollarsPerHead,
hasSite);
}
Note that UnforgivingBuilder "inherits" constants, such as MINHEAD , from
the ReservationConstants interface.
SOLUTION 15.3
Here is one solution for a builder that creates a reasonable counteroffer from an incomplete
request: