When it comes to low level design, understanding design patterns is crucial. Design patterns provide solutions to common problems that arise in software design. They offer proven and effective approaches to designing maintainable, flexible, and scalable systems.

In the context of the payment app we are developing, there are several design patterns that can be applied.

One commonly used design pattern in low level design is the Factory Method. The Factory Method pattern provides an interface for creating objects, but defers the actual instantiation to subclass implementations. This allows for flexibility in object creation and supports loose coupling between components.

Another design pattern that is frequently used is the Singleton pattern. The Singleton pattern ensures that only one instance of a class is created and provides a global point of access to that instance. This can be useful in scenarios where we need a single instance of a class throughout the system, such as for managing database connections.

Other design patterns that may be applicable in low level design include the Builder pattern, Adapter pattern, Observer pattern, and Strategy pattern.

Let's take a closer look at the Factory Method design pattern and how it can be applied in the context of our payment app.

1interface PaymentProcessor {
2  void processPayment(Payment payment);
3}
4
5class CreditCardPaymentProcessor implements PaymentProcessor {
6  public void processPayment(Payment payment) {
7    // Logic to process credit card payment
8  }
9}
10
11class PayPalPaymentProcessor implements PaymentProcessor {
12  public void processPayment(Payment payment) {
13    // Logic to process PayPal payment
14  }
15}
16
17class PaymentProcessorFactory {
18  public static PaymentProcessor createPaymentProcessor(String paymentMethod) {
19    if (paymentMethod.equals("Credit Card")) {
20      return new CreditCardPaymentProcessor();
21    } else if (paymentMethod.equals("PayPal")) {
22      return new PayPalPaymentProcessor();
23    }
24    return null;
25  }
26}

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class Main {

  public static void main(String[] args) {

    // Replace with relevant Java code here

  }

}