Real World Example of the Strategy Pattern

Question

I've been reading about the OCP principal and how to use the strategy pattern to accomplish this.

I was going to try and explain this to a couple of people, but the only example I can think of is using different validation classes based on what status an "order" is.

I've read a couple of articles online, but these don't usually describe a real like reason to use the strategy, like generating reports/bills/validation etc...

Are there any real world examples where you think a strategy pattern is common?

Answer 1

What about this:

You have to encrypt a file.

For small files, you can use "in memory" strategy, where the complete file is read and kept in memory ( let's say for files < 1 gb )

For large files, you can use another strategy, where parts of the file are read in memory and partial encrypted results are stored in tmp files.

These may be two different strategies for the same task.

The client code would look the same:

 File file = getFile();
 Cipher c = CipherFactory.getCipher( file.size() );
 c.performAction();



// implementations:
interface  Cipher  {
     public void performAction();
}

class InMemoryCipherStrategy implements Cipher { 
         public void performAction() {
             // load in byte[] ....
         }
}

class SwaptToDiskCipher implements Cipher { 
         public void performAction() {
             // swapt partial results to file.
         }

}

The

     Cipher c = CipherFactory.getCipher( file.size() );

Would return the correct strategy instance for the cipher.

I hope this helps.

( I don't even know if Cipher is the right word :P )