Liskov Substitution Principle (LSP) Explained in 100 Seconds

💡 What is Liskov Substitution Principle?

💡 The Liskov Substitution Principle (LSP), another key part of the SOLID principles, states that:

"Objects of a superclass should be replaceable with objects of its subclasses without affecting the correctness of the program."

In simple terms, if your code functions with a parent class, it should also work seamlessly with any subclass.

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🎯 Simple Example

Imagine a document editing software where users can work with different types of documents. If a user switches from a text document to a spreadsheet, they should still be able to save and print the document without learning new processes. If the spreadsheet removes the ability to save or print, the substitution breaks the system.

💡 Benefits

✅ Improved Reusability: Subclasses can replace parent classes seamlessly, making the code more adaptable.
✅ Easier Maintenance: Predictable behavior makes modifying and extending the system simpler.
✅ Greater Flexibility: New subclasses can be added without disrupting the system, supporting scalability."

🚨 Violations of LSP

⚠️ Unexpected Behavior: Substituting a subclass causes errors. For example, replacing a smartphone with one that lacks basic calling functionality.
⚠️ Method Restrictions: A subclass limits inherited functionality. For instance, a user account class that removes the ability to reset passwords when the base class allows it.
⚠️ Behavioral Inconsistency: A subclass behaves differently from the superclass. For example, a bird subclass (Penguin) that doesn’t fly while the base class expects flying.

💎 Applying LSP

👍 Ensure subclasses maintain the behavior expected by the superclass. For example, all vehicles should be able to start and stop, regardless of type.
👍 Don’t modify or reduce the functionality of inherited methods. Instead, build upon them to add new capabilities when needed.
👍 Use abstraction to separate behaviors that may not apply to all subclasses, ensuring consistency and flexibility.

📰 Others

Interested? 😃 Check out other posts from my programming principles series!

• KISS Design Principle Explained in 100 Seconds
• DRY Principle Explained in 100 Seconds
• "Tell, Don't Ask" Principle Explained in 100 Seconds

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