Beginner LevelSoftware Engineering Principles
1. Explain the 5 SOLID Principles of Object-Oriented Software Design with practical refactoring examples.
❓ Context: Detail Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion principles.
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S (Single Responsibility): A class should have one, and only one, reason to change.
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O (Open/Closed): Software entities should be open for extension, but closed for modification.
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L (Liskov Substitution): Subtypes must be substitutable for their base types without altering correctness.
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I (Interface Segregation): Clients should not be forced to depend on methods they do not use.
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D (Dependency Inversion): High-level modules should depend on abstractions, not concrete implementations.
typescript
// ❌ Violating Dependency Inversion
class OrderProcessorBad {
private mysqlDb = new MySQLDatabase(); // Tight coupling
processOrder(orderId: string) {
this.mysqlDb.saveOrder(orderId);
}
}
// ✅ SOLID: Applying Dependency Inversion & Open/Closed
interface OrderRepository {
saveOrder(orderId: string): void;
}
class PostgresOrderRepository implements OrderRepository {
saveOrder(orderId: string) {
console.log('Saving order \\${orderId} to PostgreSQL');
}
}
class OrderProcessorGood {
constructor(private repo: OrderRepository) {} // Injected abstraction
processOrder(orderId: string) {
this.repo.saveOrder(orderId);
}
}💡Refactoring code to conform to SOLID Dependency Inversion Principle.
🎯 Interview Key Takeaway
Applying SOLID principles reduces code coupling, improves unit test coverage, and extends code maintainability.
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