Impact of Program Design Practice Test

A bank is revising its Online Banking Application after an audit found inconsistent balance changes across features. The redesign emphasizes encapsulation using three classes: BankAccount, Transaction, and CustomerProfile. BankAccount stores balance as a private field and exposes deposit and withdraw methods that validate amounts and create a Transaction record for every change. CustomerProfile holds customer information and a list of accounts, but it cannot edit balances directly; it must call account methods. A separate TransferService moves money by calling withdraw on one BankAccount and deposit on another, relying on the built-in validation. The team also adds SavingsAccount extends BankAccount with a minimumBalance rule, overriding withdraw to block withdrawals that break the rule. This keeps account-specific constraints close to the account type. Readability improves because balance changes happen in one place, and maintainability improves because new rules are added by editing BankAccount or a subclass, not every feature. The team accepts a slight performance cost from extra method calls because it prevents invalid balance updates that would be expensive to fix later. Considering the class design, in the scenario, how does encapsulation improve data security?

Considering the class design, a game studio is building a 2D adventure game where players explore levels and fight enemies. The design centers on three classes: GameCharacter, Player, and Enemy. GameCharacter is a superclass that stores private health and position fields and provides methods like takeDamage(amount), move(dx, dy), and isAlive(). Player and Enemy inherit from GameCharacter. Player adds an inventory and a method useItem(item), while Enemy adds an aiType and a method chooseAction(). The team also created an abstract class Attack with an abstract method apply(GameCharacter target). Specific attacks like MeleeAttack and FireballAttack extend Attack and implement apply differently. During combat, CombatSystem stores a list of Attack objects and calls apply on each one without checking its exact type. This keeps combat code short and readable, because CombatSystem does not need separate if-statements for every attack. When designers add a new attack later, they only create a new subclass of Attack; they do not change CombatSystem. The team notes that good class design also helps performance by avoiding repeated code paths and reducing unnecessary checks. Based on the scenario, how does polymorphism in the described classes benefit the program?