Simplified transcript
Object-oriented programming gives us useful tools such as:
- Inheritance
- Encapsulation
- Polymorphism
These tools help us build complex software. However, simply knowing how to use them does not guarantee good software.
If we use them carelessly, our software can become:
- Easy to break
- Difficult to change
- Hard to reuse
- Difficult to understand
This is why we need design principles. Design principles guide us in deciding when and how to use object-oriented concepts properly. They help us avoid common mistakes and create software that is easier to understand, change, test, and reuse.
Enhanced explanation
Think of OOP concepts as building materials:
- Inheritance lets one class receive behaviour from another.
- Encapsulation protects an object’s internal data and rules.
- Polymorphism allows different objects to respond differently to the same action.
Having good building materials does not automatically produce a well-designed building. You must also know how to arrange and connect them.
Design principles provide that guidance.
For example, inheritance can reduce repeated code, but using it everywhere can tightly connect classes. A small change in a parent class might then unexpectedly affect many child classes.
Design principles help us recognize and avoid problems like this.
What does “quality software” mean?
Quality software is generally:
- Easy to understand: Another developer can follow the code.
- Easy to modify: A new requirement does not require rewriting everything.
- Less fragile: Changing one part does not unexpectedly break another.
- Reusable: Parts of the software can work in other places.
- Testable: Individual parts can be checked separately.
Main lesson
OOP gives us the tools to build software. Design principles teach us how to use those tools properly.
Knowing inheritance, encapsulation, and polymorphism is the starting point. The next level is learning how to combine them without making the system complicated or fragile.