Understanding Design Patterns

When designing a complex application like a payment app, it's important to apply design patterns to ensure the application is efficient, maintainable, and scalable. Design patterns are reusable solutions to common problems that occur during software design.

One of the commonly used design patterns in low-level design is the Singleton design pattern. The Singleton pattern ensures that only one instance of a class is created and provides a global point of access to that instance.

The Singleton pattern can be useful in scenarios like establishing a database connection, where only a single connection instance is required throughout the application.

1class DatabaseConnection {
2  private static DatabaseConnection instance;
3  
4  private DatabaseConnection() {
5    // Database connection setup code
6    System.out.println("Database connection established");
7  }
8  
9  public static DatabaseConnection getInstance() {
10    if (instance == null) {
11      instance = new DatabaseConnection();
12    }
13    return instance;
14  }
15}
16
17// Usage
18DatabaseConnection conn1 = DatabaseConnection.getInstance();
19DatabaseConnection conn2 = DatabaseConnection.getInstance();
20
21if (conn1 == conn2) {
22  System.out.println("conn1 and conn2 are the same instance");
23}

In the above example, the DatabaseConnection class is designed as a Singleton. The private constructor ensures that the class cannot be instantiated directly, and the getInstance() method provides the single instance. The first call to getInstance() creates the instance, and subsequent calls return the already created instance.

Understanding and utilizing design patterns like the Singleton pattern can greatly enhance the quality and maintainability of the code. It's important to have a good understanding of various design patterns and choose the appropriate ones based on the application's requirements and constraints.

Try running the above Java code example to see how the Singleton pattern works in practice.

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}

class Main {

  public static void main(String[] args) {

    // Replace with your Java logic here

    // Example of Singleton design pattern

    DatabaseConnection conn1 = DatabaseConnection.getInstance();

    DatabaseConnection conn2 = DatabaseConnection.getInstance();

    if (conn1 == conn2) {

      System.out.println("conn1 and conn2 are the same instance");

    }

  }

}

​

class DatabaseConnection {

  // Private static instance

  private static DatabaseConnection instance;

  // Private constructor

  private DatabaseConnection() {

    // Database connection setup code

    System.out.println("Database connection established");

  }

  // Public static method to get instance

  public static DatabaseConnection getInstance() {

    if (instance == null) {

      instance = new DatabaseConnection();

    }

    return instance;