Strategy pattern in PHP - Mini Project: Build & Apply

Implementing the Strategy Pattern in PHP

📖 Scenario: Imagine you are building a payment system for an online store. The store wants to support multiple payment methods like credit card and PayPal. Each payment method has a different way to process payments.

🎯 Goal: You will create a simple PHP program that uses the Strategy pattern to switch between different payment methods easily. This will help the store process payments using different strategies without changing the main code.

📋 What You'll Learn

Create an interface for payment methods

Implement two payment method classes: CreditCardPayment and PayPalPayment

Create a PaymentContext class that uses a payment strategy

Demonstrate switching payment methods and processing payments

💡 Why This Matters

🌍 Real World

The Strategy pattern is used in software where you want to switch between different algorithms or behaviors easily, like payment processing, sorting methods, or logging strategies.

💼 Career

Understanding design patterns like Strategy is important for writing flexible and maintainable code, a key skill for software developers and engineers.

1

Create the PaymentMethod interface

Create an interface called PaymentMethod with a public method pay that accepts a parameter amount.

PHP

# Your code here

Need a hint?

Use the interface keyword to define the PaymentMethod interface with the pay method.

2

Implement CreditCardPayment and PayPalPayment classes

Create two classes called CreditCardPayment and PayPalPayment that implement the PaymentMethod interface. Each class should have a pay method that prints a message showing the payment method and the amount paid.

PHP

<?php
interface PaymentMethod {
    public function pay(float $amount): void;
}

# Your code here

Need a hint?

Implement the pay method in both classes to print the payment details.

3

Create the PaymentContext class

Create a class called PaymentContext with a private property paymentMethod of type PaymentMethod. Add a constructor that accepts a PaymentMethod and assigns it to paymentMethod. Add a public method setPaymentMethod to change the payment method. Add a public method pay that accepts an amount and calls the pay method of the current paymentMethod.

PHP

<?php
interface PaymentMethod {
    public function pay(float $amount): void;
}

class CreditCardPayment implements PaymentMethod {
    public function pay(float $amount): void {
        echo "Paid $amount using Credit Card.\n";
    }
}

class PayPalPayment implements PaymentMethod {
    public function pay(float $amount): void {
        echo "Paid $amount using PayPal.\n";
    }
}

# Your code here

Need a hint?

Use a private property to hold the current payment method and methods to set it and pay.

4

Use PaymentContext to process payments

Create a PaymentContext object with CreditCardPayment as the initial payment method. Call the pay method with amount 100.0. Then change the payment method to PayPalPayment using setPaymentMethod and call pay again with amount 200.0. Print the output.

PHP

paymentMethod = $paymentMethod;
    }

    public function setPaymentMethod(PaymentMethod $paymentMethod): void {
        $this->paymentMethod = $paymentMethod;
    }

    public function pay(float $amount): void {
        $this->paymentMethod->pay($amount);
    }
}

# Your code here

Need a hint?

Create the context with CreditCardPayment, pay 100, switch to PayPalPayment, then pay 200.