Definition
The Strategy pattern involves separating an algorithm from its host class and putting it in a separate class. When there are multiple strategies available for an algorithm, for a given problem it is always better to separate them into different objects. If the algorithms are all kept in the one class, the class will be become a big messy conditional statement.
The Strategy pattern enables a client to choose which algorithm to use from a family of algorithms and gives it a simple way to access it.
Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from the clients that use it.
Note:
- Strategy is like Template Method except that strategy has details whereas template provides skeleton for the algorithm.
- State is like Strategy except in its objective.
- Strategy lets us change the internal object. Decorator lets us change the covering; the underlying object remains same.
Design
Let us say that we are implementing text hashing for the system. During the requirements definition the decision is to implement the MD5 hashing, then during development SHA1 was added for another requirement, and it kept continuing. Finally decision is to implement with a couple of options and based on the client strategy it can be changed.
UML Diagram
Code
public abstract class HashingStrategy
{
public abstract void HashingInterface(string text);
}
public class MD5Hashing : HashingStrategy
{
public override void HashingInterface(string text)
{
MD5 md5 = new MD5CryptoServiceProvider();
Byte[] bytes;
bytes = ASCIIEncoding.Default.GetBytes(text);
Byte[] encodedBytes;
encodedBytes = md5.ComputeHash(bytes);
string A = BitConverter.ToString(encodedBytes);
}
}
public class HashingContext
{
private HashingStrategy _hashingStrategy;
public HashingContext(HashingStrategy hashingStrategy)
{
_hashingStrategy = hashingStrategy;
}
public void HashPassword(string text)
{
_hashingStrategy.HashingInterface(text);
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