Design Patterns Java™ Workbook

Chapter 22. State

The state of an object is a combination of the current values of its attributes. When you call a set- method, you typically change an object's state, and an object can change its own state as its methods execute.

In some cases, an object's state can be a prominent aspect of its behavior, such as when modeling transactions and machines. Logic that depends on the object's state may spread through many of the class's methods. To counter this spread, you can move state-specific behavior into a group of classes, with each class representing a different state. This lets you avoid having deep or complex if statements, relying instead on polymorphism to execute the right implementation of an operation. The intent of the STATE pattern ...