$($java$)$Demo $-$ Strategy Pattern

PaymentStategy Interface

package StrategyPatternDemoOne;

$//$ Strategy interface

interface PaymentStrategy $\{$

void pay$($double amount$)$;

$\}$

package StrategyPatternDemoOne;

class PayPalStrategy implements PaymentStrategy $\{$

private String email;

private String password;

public PayPalStrategy$($String email, String password$)\{$

this.email $=$ email;

this.password $=$ password;

$\}$

public void pay$($double amount$)\{$

System.out.println$("$Paying $"+$ amount $+"$ with PayPal."$)$;

$//$ Perform the payment logic using PayPal credentials

$\}$

$\}$

package StrategyPatternDemoOne;

$//$ Concrete strategies

class CreditCardStrategy implements PaymentStrategy $\{$

private String cardNumber;

private String expiryDate;

private String cvv;

public CreditCardStrategy$($String cardNumber, String expiryDate, String cvv$)\{$

this.cardNumber $=$ cardNumber;

this.expiryDate $=$ expiryDate;

this.cvv $=$ cvv;

$\}$

public void pay$($double amount$)\{$

System.out.println$("$Paying $"+$ amount $+"$ with credit card."$)$;

$//$ Perform the payment logic using credit card details

$\}$

$\}$

package StrategyPatternDemoOne;

$//$ Client code

class ShoppingCart $\{$

private PaymentStrategy paymentStrategy;

public void setPaymentStrategy$($PaymentStrategy paymentStrategy$)\{$

this.paymentStrategy $=$ paymentStrategy;

$\}$

public void checkout$($double amount$)\{$

$//$ Perform the checkout process

paymentStrategy.pay$($amount$)$;

$\}$

$\}$

Driver:

package StrategyPatternDemoOne;

public class Driver $\{$

$//$ Usage

public static void main$($String$[]$ args$)\{$

ShoppingCart cart $=$ new ShoppingCart$()$;

$//$ Set the payment strategy dynamically

cart.setPaymentStrategy$($new CreditCardStrategy$("1234567890123456","12/23","123"))$;

cart.checkout$(100\mathrm{.}0)$;

$//$ Change the payment strategy at runtime

cart.setPaymentStrategy$($new PayPalStrategy$("$example@example.com", "password"$))$;

cart.checkout$(50\mathrm{.}0)$;

$\}$

$\}$

Open image$-20230711-134214.$png

In the example above, the PaymentStrategy interface defines a contract for payment strategies, and CreditCardStrategy and PayPalStrategy are concrete implementations of the payment algorithm. The ShoppingCart class contains a reference to a PaymentStrategy object, which can be set dynamically. The client code can change the payment strategy by calling the setPaymentStrategy$()$ method.

By applying the Strategy pattern, the client code can switch between different payment strategies without modifying the core logic of the ShoppingCart class. This flexibility is especially useful when you have multiple algorithms or behaviors that need to be dynamically selected or replaced based on varying requirements.