Practical use of the Strategy template

Brief Definition of the Strategy Template

Practical examples of applying the Strategy template

• Sorting: We want to sort these numbers, but we don’t know if we will use BrickSort, BubbleSort or any other sorting. For example, you have a website on which a page displays elements based on popularity. However, many things can be “Popular” (most views, most subscribers, creation date, most activity, least comment). In case the management does not yet know exactly how to place an order, and may want to experiment with different orders at a later date, you create an interface (IOrderAlgorithm or something else) with the order method and allow the Orderer object to delegate the order of the concrete implementation of the IOrderAlgorithm interface . You can create CommentOrderer, ActivityOrderer, etc., and simply turn them off when new requirements appear.
• Processing a queue from heterogeneous objects (queue processing and saving data): An example would be a proxy system that accumulates objects from different data sources, then after extracting an object from the queue and then saving it, it is determined by the selection strategy based on the properties of this object.
• Validation We need to check the elements in accordance with the “Some Rule”, but it is not yet clear what this rule will be, and we can think of new ones.
• Authentication: Select an authentication strategy between Basic, Digest, OpenID, OAuth schemes.

interface AuthStrategy {
    auth(): void;
}
class Auth0 implements AuthStrategy {
    auth() {
        log('Authenticating using Auth0 Strategy')
    }
}
class Basic implements AuthStrategy {
    auth() {
        log('Authenticating using Basic Strategy')
    }
}
class OpenID implements AuthStrategy {
    auth() {
        log('Authenticating using OpenID Strategy')
    }
}

class AuthProgram {
    private _strategy: AuthStrategy
    use(strategy: AuthStrategy) {
        this._strategy = strategy
        return this
    }
    authenticate() {
        if(this._strategy == null) {
            log("No Authentication Strategy set.")
        }
        this._strategy.auth()
    }
    route(path: string, strategy: AuthStrategy) {
        this._strategy = strategy
        this.authenticate()
        return this
    }
}

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• (logging): Log4Net Log4j , Appenders, Layouts, and Filters.
• Encrypting: for small files, you can use the in-memory strategy when the entire file is read and stored in memory (say, for files <1 GB). For large files, you can use a different strategy where parts of the file are read in memory and partially encrypted results are stored in tmp files. These can be two different strategies for the same task.

//   ""
interface  Cipher  {
     public void performAction();
}

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

class SwaptToDiskCipher implements Cipher { 
         public void performAction() {
             //     .... 
         }

}

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

• Graphic editor: for example, in the Windows Paint application there is an implementation of a strategy template in which you can independently select the shape and color in different sections. Here, shape and color are algorithms that can be changed at runtime.

Shape redCircle = new RedCircle(); //    «»
Shaped redCircle = new Shape("red","circle"); //   «»

SOLID and implementation of the Strategy template

class Document {...}
class Printer {
    print(doc: Document, printStyle: Number) {
        if(printStyle == 0 /*   */) {
            // ...
        }
        if(printStyle == 1 /*  */) {
            // ...            
        }
        if(printStyle == 2 /*     */) {
            // ...
        }
        if(printStyle == 3 /*     */) {
            // ...            
        }
        if(printStyle == 4 /*     */) {
            // ...
        }
        // ...
    }
}

class Document {...}
interface PrintingStrategy {
    printStrategy(d: Document): void;
}
class ColorPrintingStrategy implements PrintingStrategy {
    printStrategy(doc: Document) {
        log(" ")
        // ...
    }
}
class InvertedColorPrintingStrategy implements PrintingStrategy {
    printStrategy(doc: Document) {
        log("  ")
        // ...
    }
}
class Printer {
    private printingStrategy: PrintingStrategy
    print(doc: Document) {
        this.printingStrategy.printStrategy(doc)
    }
}

//  /
interface LockOpenStrategy {
    open();
    lock();
}
//      
class RetinaScannerLockOpenStrategy implements LockOpenStrategy {
    open() {
        //...
    }
    lock() {
        //...
    }
}

//       
class KeypadLockOpenStrategy implements LockOpenStrategy {
    open() {
        if(password != ""){
            log("Entry Denied")
            return
        }
        //...
    }
    lock() {
        //...
    }
}
//        .
abstract class Door {
    public lockOpenStrategy: LockOpenStrategy
}
//   .
class GlassDoor extends Door {}
//    .
class MetalDoor extends Door {}
//       .
class DoorAdapter {
    openDoor(d: Door) {
        d.lockOpenStrategy.open()
    }
}

var glassDoor = new GlassDoor(); //   
glassDoor.lockOpenStrategy = new RetinaScannerLockOpenStrategy(); //         
var metalDoor = new MetalDoor(); //     
metalDoor.lockOpenStrategy = new KeypadLockOpenStrategy(); //      .
var door1 = new DoorAdapter().openDoor(glassDoor); //    . 
var door2  = new DoorAdapter().openDoor(metalDoor); //    . 

Refactoring and Strategy Template