Mastering SOLID Principles in Software Development with Real-World Analogies - Part 2

In Part 1, we got to know about what are SOLID principles in software development, and three of the principles that make up the acronym SOLID: this includes Sin

In Part 1, we got to know about what are SOLID principles in software development, and three of the principles that make up the acronym SOLID: this includes Sin

In Part 1, we got to know about what are SOLID principles in software development, and three of the principles that make up the acronym SOLID: this includes Single Responsibility Principle (SRP), Open/Closed Principle (OCP), and Liskov Substitution Principle (LSP). In Part 2, we will look at the other two principles: Interface Segregation Principle (ISP), Dependency Inversion Principle (DIP). So let’s check it out! 

4. Interface Segregation Principle (ISP)

Clients should not be forced to depend on interfaces they do not use.

The Interface Segregation Principle (ISP) encourages designing small, specific interfaces rather than large, general-purpose ones. This makes it easier to implement only the required methods and prevents classes from being burdened by unnecessary functionality.

Real-World Analogy:

Here’s how implementing ISP in Object-Oriented Design works! Think about different types of remote controls. A TV remote has buttons for changing channels and volume, while an air conditioner remote has buttons for temperature control and fan speed. If you had a universal remote with all possible buttons, it would be confusing and harder to use. Instead, each remote has only the controls it needs.

Explanation:

ISP advocates breaking down large interfaces into smaller ones that are more specific to the needs of their clients. This leads to cleaner, more maintainable code, as classes aren’t forced to implement methods they don’t need.

Without Interface Segregation Principle

abstract class PaymentProcessor {

  void processCreditCardPayment(double amount);

  void processPaypalPayment(double amount);

  void processBitcoinPayment(double amount);

}

class CreditCardPayment implements PaymentProcessor {

  @override

  void processCreditCardPayment(double amount) {

    // Process credit card payment

  }

  @override

  void processPaypalPayment(double amount) {

    // Not implemented

  }

  @override

  void processBitcoinPayment(double amount) {

    // Not implemented

  }

}

Explanation:

In this version, the PaymentProcessor interface defines methods for processing multiple types of payments: credit card, PayPal, and Bitcoin. However, the CreditCardPayment class only implements credit card payments. The other methods (processPaypalPayment and processBitcoinPayment) are not needed and remain unimplemented, violating the Interface Segregation Principle (ISP).

The Interface Segregation Principle suggests that no class should be forced to implement methods it does not need. By having a general PaymentProcessor interface with multiple payment methods, we are imposing unnecessary requirements on classes like CreditCardPayment, leading to unused or empty methods, making the design inefficient.

With Interface Segregation Principle

abstract class CreditCardPaymentProcessor {

  void processCreditCardPayment(