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Adavantages of Liskov Substitution Principle

Code Reusability and Reduced Duplication

LSP, by virtue of its nature, fosters reusability. You can use the superclass object and substitute it with any of its subclasses without worrying about the system behaving unexpectedly.

Let's reference the code we used in the previous section to understand this.

abstract class PaymentProcessor {
abstract processPayment(amount: number): void;

class CreditCardProcessor extends PaymentProcessor {
processPayment(amount: number): void {
console.log(`Processing credit card payment of $${amount}`);
// implementation details for processing credit card payment...

class DebitCardProcessor extends PaymentProcessor {
processPayment(amount: number): void {
console.log(`Processing debit card payment of $${amount}`);
// implementation details for processing debit card payment...

class PayPalProcessor extends PaymentProcessor {
processPayment(amount: number): void {
console.log(`Processing PayPal payment of $${amount}`);
// implementation details for processing PayPal payment...

function executePayment(paymentProcessor: PaymentProcessor, amount: number) {

// Now, we can process payments using any of the payment methods:

const creditCardProcessor = new CreditCardProcessor();
executePayment(creditCardProcessor, 100);

const debitCardProcessor = new DebitCardProcessor();
executePayment(debitCardProcessor, 200);

const payPalProcessor = new PayPalProcessor();
executePayment(payPalProcessor, 300);

All payment processors share the processPayment method. If we need to add another type of payment processor, we don't need to reimplement processPayment from scratch. Instead, we just extend the PaymentProcessor class and provide a specific implementation for the new payment method. This way, we're reusing the existing class structure and reducing code duplication.

Enhanced Flexibility

The LSP allows you to make your code more flexible. You can introduce new subclasses without breaking existing functionality, because the contract defined by the superclass is honored by all subclasses.

If we want to add a new payment method, we can easily do so by extending the PaymentProcessor class and providing the specific implementation. The rest of the system can remain the same and still work with the new payment processor, demonstrating the flexibility of the design.

Let's say we want to add support for Bitcoin payments. We'd create a new class BitcoinProcessor that extends the PaymentProcessor class:

class BitcoinProcessor extends PaymentProcessor {
processPayment(amount: number): void {
console.log(`Processing Bitcoin payment of ${amount} BTC`);
// Implementation details for processing Bitcoin payment...

Now we can use BitcoinProcessor in the same way as any other PaymentProcessor:

const bitcoinProcessor = new BitcoinProcessor();
executePayment(bitcoinProcessor, 2); // Process a payment of 2 BTC

The executePayment function and any other part of the system that uses PaymentProcessor objects can work with BitcoinProcessor without any changes. This is the power and flexibility provided by adhering to the Liskov Substitution Principle.

Lower Maintenance Cost

Codebases adhering to the LSP are easier to maintain. Changes to the superclass or subclass will be straightforward because the substitutability ensures a level of consistency in behavior.

Changes to how a specific payment method is processed only require changes to the corresponding class, not to the executePayment function or any other part of the system that uses PaymentProcessor objects. This containment of changes makes the system easier to maintain.

Improved Robustness

Because each payment processor adheres to the Applications are less prone to errors and unexpected behavior because the LSP helps avoid certain design anomalies that might arise from improper subclassing.

Because each payment processor adheres to the contract defined by the PaymentProcessor class, we can be sure that they will behave as expected. This reduces the risk of errors and unexpected behavior.

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Increased Understanding and Ease of Use

If subclasses can truly substitute for their base classes, developers can confidently use subclasses in place of their base class, leading to increased understanding and ease of use when working with a hierarchy of classes.

It's clear from the class structure that all payment processors can process a payment. This makes the system easy to understand and use - we don't need to worry about the specifics of each payment method when we're writing code that uses payment processors.


Adhering to the LSP often leads to more modular code, since it encourages creating substitutable parts for complex systems. This can make the overall software design cleaner and easier to understand.

The system is made up of interchangeable PaymentProcessor objects. This modular design makes it easy to adjust the system as needed, for example by adding or removing payment methods.

In this way, the Liskov Substitution Principle helps us create a system that is flexible, robust, easy to understand and maintain, and well-structured.

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