CSC/ECE 517 Fall 2012/ch1b 2w41 dc

State pattern and the related patterns

The State pattern allows an object to completely change its behavior and the change depends on its current internal state. Alternatively, a monolithic object's behavior is a function of its state, and it must change its behavior at run-time depending on that state. State pattern is closely related to Strategy pattern and Bridge pattern. We shall discuss the three patterns, their structures, advantages & disadvantages.

Description

The state pattern is behavioral as it defines how communication between classes or entities is controlled. It is used in programming to define the state of an object. This pattern, also called as object for states pattern <ref>http://en.wikipedia.org/wiki/State_pattern State pattern</ref>, allows the class of an object to change at runtime without changing the interface used to access the object or losing the current state. This change in class is abstracted with the use of a wrapper object or context.<ref>http://www.blackwasp.co.uk/State.aspx</ref> Creating object oriented state machines is one of the uses of the state pattern. In this, the functionality of the object changes fundamentally according to its state. Using multiple concrete classes, each class inheriting from the same base class is an alternative to multiple number of 'if' or 'switch' statements.