Creational Patterns in Banking

Welcome back! You've learned so much about creational patterns, and it's time to apply what you know to a real-world project: a banking system. In this unit, we'll focus on using creational patterns to manage and simplify the creation of banking system components.

Before we dive in, let's quickly recap the creational patterns we'll use:

1. Singleton Pattern: Ensures a class has only one instance and provides a global point of access to it.
2. Factory Method Pattern: Defines an interface for creating an object but lets subclasses alter the type of objects that will be created.
3. Abstract Factory Pattern: Provides an interface for creating families of related or dependent objects without specifying their concrete classes.
4. Builder Pattern: Separates the construction of a complex object from its representation, allowing the same construction process to create various representations.

We will implement these patterns to create a logger, accounts, and account factories for our banking system.

Let's see what you'll build in this unit. You will create:

1. Logger with the Singleton Pattern: A logging mechanism that ensures only one instance of the logger exists throughout the application.
2. Accounts using the Factory Method Pattern: Different types of accounts (savings and current) created via a factory method.
3. Account Factories using the Abstract Factory Pattern: Factories that will instantiate different types of accounts.
4. Code Integration: Comprehensive integration of these patterns into a cohesive system.

First, let's create a logger using the Singleton Pattern. In TypeScript, we can use a class with a private static instance and a private constructor to ensure that only one instance of the logger exists throughout the application.

class Logger {
    private static instance: Logger;

    private constructor() {}

    public static getInstance(): Logger {
        if (!Logger.instance) {
            Logger.instance = new Logger();
        }
        return Logger.instance;
    }

    public log(message: string): void {
        console.log(message);
    }
}

Here, the Logger class uses a private static property to hold the singleton instance. The constructor is private, so new instances cannot be created from outside the class. The getInstance method returns the single instance, creating it if it doesn't exist. The log method outputs messages.