Head First Design Patterns, 2nd Edition

Chapter 10. The State of Things: The State Pattern

A little-known fact: the Strategy and State Patterns are twins separated at birth. You’d think they’d live similar lives, but the Strategy Pattern went on to create a wildly successful business around interchangeable algorithms, while State took the perhaps more noble path of helping objects to control their behavior by changing their internal state. As different as their paths became, however, underneath you’ll find almost precisely the same design. How can that be? As you’ll see, Strategy and State have very different intents. First, let’s dig in and see what the State Pattern is all about, and then we’ll return to explore their relationship at the end of the chapter.

Java Breakers

Gumball machines have gone high tech. That’s right, the major manufacturers have found that by putting CPUs into their candy machines, they can increase sales, monitor inventory over the network, and measure customer satisfaction more accurately.

But these manufacturers are gumball machine experts, not software developers, and they’ve asked for your help:

Note

At least that’s their story—we think they just got bored with the circa 1800s technology and needed to find a way to make their jobs more exciting.

Cubicle Conversation

Judy: ...