Design Patterns Java™ Workbook

Chapter 23. Strategy

private Advisor getAdvisor()
{
if (advisor == null)
{
if (PromotionAdvisor.singleton.hasItem())
{
advisor = PromotionAdvisor.singleton;
}
else if (isRegistered())
{
advisor = GroupAdvisor.singleton;
}
else if (isBigSpender())
{
advisor = ItemAdvisor.singleton;
}
else
{
advisor = RandomAdvisor.singleton;
}
}
return advisor;
}

private boolean isBigSpender()
{
Calendar cal = Calendar.getInstance();
cal.add(Calendar.YEAR, -1);
return
spendingSince(cal.getTime()) > BIG_SPENDER_DOLLARS;
}

CHALLENGE 23.4

Write the code for Customer.getRecommended().

CHALLENGE 23.5

In the new design, four singletons implement the Advisorinterface in four ways,

encapsulating four strategies. Is the presence of multiple similar singletons

reminiscent of a design pattern?

Comparing Strategy and State................................................................................................................

The refactored code consists almost entirely of simple methods in simple classes. This is an
advantage in its own right and makes adding new strategies easy. The refactoring relies
primarily on the idea of distributing an operation across a related group of classes. In this
regard, STRATEGY is identical to STATE. In fact, many developers wonder whether these are
really different patterns.

On the one hand, in the real world, strategies (such as recommending a firework) and states
(such as a carousel door with a one-touch control button) are clearly different ideas. This real