Strategy pattern in a nutshell

The strategy pattern is a behavioural pattern. According to Wikipedia is  also known as the policy pattern (not sure by whom, but Wikipedia holds a lot of untold truths)

The book definition reads:

Defines a set of encapsulated algorithms that can be swapped to carry out a specific behaviour

 

To be able to use this pattern properly, take a minute to think about this three things:

1. Isolate the behaviors you need and define an interface that applies to all of them.
2. Implement the different behaviors. Each behavior IMPLEMENTS the interface.
3. The main object HAS-A behavior interface container from which the selected behavior will be called.

Diagram:

Where Would I Use This Pattern?

The Strategy pattern is to be used where you want to choose from algorithms used at runtime

 

Some examples where you may find this pattern:

• Save to different formats
• Payment methods
• Sorting algorithms
• File compression

 

References:

http://en.wikipedia.org/wiki/Strategy_pattern