SOLID Simplified - Software Design Fundamentals

Explain that a class should have one responsibility, not one method. Show why calculateBonus belongs to HR, not the employee class, highlighting one reason to change.

Move unrelated responsibilities to dedicated classes to enforce single responsibility; HRPersonnel uses Employee, while FinanceCalculations uses EmployeeBenefits to compute bonuses.

Single responsibility means a module has one and only one responsibility. Methods do one task; components handle a single concern like configuration data, guided by cohesion.

Enforce the open-closed principle to keep existing functionality intact while adding new criteria, avoiding multiple software versions, costly maintenance, and fragile, hard-to-test changes.

this lecture demonstrates separating bonus and ESOP calculations into dedicated interfaces to achieve open closed principle compliance for varying criteria.

Explore the Liskov substitution principle by relating an employee and IBenefitsCalculator hierarchy through a grade-based calculator, and examine how introducing contractors can violate LSP when overridden methods throw exceptions.

Explore how type checks to avoid method exceptions reveal fragile inheritance, violate the open-closed principle, and risk breaking client code on base class references in solid design.

Examine how derived classes violate the Liskov substitution principle by tightening or relaxing preconditions and breaking input and return value contracts under design by contract.

Refactor the employee hierarchy by moving getGrade and isServingNotice to a Regular class. Enforce base class contracts and use derived references for predictable client behavior.

Master the Liskov Substitution Principle, ensuring derived classes remain substitutable for base classes and respect design by contract. Address violations by adjusting contracts or inheritance, and uphold open-closed principle.

Understand the interface segregation principle by analyzing a fat employee interface that forces dummy implementations for unused training methods, highlighting how distinct interfaces improve design and maintainability.

Explore interface segregation by modeling an employee as an interface with name, id, and address; avoid fat interfaces that cause Liskov substitution principle violations.

Apply the interface segregation principle to expose only interfaces clients use. Avoid unnecessary dependencies and relate to the Liskov Substitution Principle and the Single Responsibility Principle.

Examine the dependency inversion principle by showing how high level modules depend on abstractions rather than details, and how salary calculator relies on interface-based tax and bonus calculators.

Revisit the solid principle definition by showing how high and low level modules depend on abstractions. Contrast interfaces with concrete implementations to highlight that abstraction should not depend on details.

Invert dependencies to maximize reuse by moving the abstraction, namely the bonus calculator interface, into the same library as the salary calculator, enabling independent implementations and stable interfaces.