Extras/Practice Everything

Section 1: Class Basics

• Product.getDescription() returns {name}: ${price} (example: Mug: $12)
• ShoppingCart starts empty; addItem appends; getTotal sums prices
• Example: Mug 12 + Notebook 8 → total 20

Section 2: Private Fields & Defaults

• BankAccount starts at balance 0 when constructed with no args
• deposit / withdraw change balance; getBalance returns it
• Example: deposit 50, withdraw 10 → balance 40
• Config defaults: host = 'localhost', port = 3000, role = 'user'

Section 3: Interfaces

• CreditCard.pay(25) → Paid $25 with card 1234 (for card '1234')
• PayPal.pay(25) → Paid $25 with PayPal user@example.com

Section 4: Programming to Abstractions

• processPayment(method, amount) returns that method's payment result for the amount
• GiftCard with code 'GC-001': pay(40) → Paid $40 with gift card GC-001

Section 5: Inheritance

• Package.getLabel() → {label} ({weight}kg)
• Example: new Box('Box A', 5, 10).getLabel() → Box A (5kg)
• Example: new Crate('Crate B', 20, 'wood').getLabel() → Crate B (20kg)

Section 6: Method Overriding

• Shape.getArea() → 0
• new Circle(2).getArea() is about 12.57 (π × radius²)
• new Rectangle(3, 4).getArea() → 12

Section 7: Substitutability

• MediaPlayer.playFile accepts MediaFile and returns that file's play result
• Audio example: Playing audio song.mp3
• Video example: Playing video movie.mp4

Section 8: Composition & Dependency Injection

• Logger.log(message) returns the prefixed string Log: {message}
• InMemoryLogger stores the raw message argument (not the prefixed return value); getLogs() returns a copy of those stored messages
• ReportService.generateReport('Weekly Summary') calls the injected logger with Report: Weekly Summary
• After that call with an InMemoryLogger, getLogs() includes Report: Weekly Summary (the argument that was logged)