--- title: "KUKL customer system design and code" subject: "Object Oriented Analysis and Design" chapter: 4 key: "semester_6/object_oriented_analysis_and_design:kukl-use-case-class-diagram-code" source: https://www.bctengineer.com/q/semester_6/object_oriented_analysis_and_design/kukl-use-case-class-diagram-code site: BCT Engineering --- # KUKL customer system design and code Object Oriented Analysis and Design · Chapter 4: Implementation - Asked in: 2071 Magh, 13 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/object_oriented_analysis_and_design/kukl-use-case-class-diagram-code - Whole chapter: https://www.bctengineer.com/md/semester_6/object_oriented_analysis_and_design/chapter-4 ## Question Kathmandu Upatyaka Khane Pani Limited (KUKL) has hired you as a system analyst of an online customer management system and payment system. The system keeps track of all the customers and the payment they make for the service provided. The system has the option for electronic payment. Analyze and prepare the use case and design class diagram for the system. Map the design into code. ## Short answer Use case diagram: Customer, Staff, Admin, Payment Gateway actors; Register Connection, View Bill, Pay Bill (extended by Pay Electronically) etc. Class diagram: Customer–Bill 1–*, Bill–Payment 1–*, with CashPayment/ElectronicPayment subclasses. Code uses collections for associations and polymorphic payment processing. ## Answer **Assumptions:** customers are registered with a connection; bills are generated monthly from meter readings; payment is made either in cash at the counter or electronically (card/e-wallet). Actors: Customer, Cashier/Staff, Admin, Payment Gateway (external). #### Use case diagram ```text +------------------------------+ | KUKL Customer Management | [Customer] --|-( Register Connection ) | [Customer] --|-( View Bill ) | [Customer] --|-( Pay Bill ) | | ^ <> | | | | | ( Pay Electronically )------|--[Payment Gateway] [Customer] --|-( View Payment History ) | [Staff] -----|-( Record Meter Reading ) | [Staff] -----|-( Generate Bill ) | [Staff] -----|-( Accept Cash Payment ) | [Admin] -----|-( Manage Customers ) | [Admin] -----|-( Generate Reports ) | +------------------------------+ ``` `Pay Bill` is extended by `Pay Electronically` (an optional choice of payment mode). All customer use cases `<>` a `Login` use case, which is left out of the diagram for clarity. #### Design class diagram ```text +---------------+ 1 * +----------------+ | Customer |--------| Bill | |---------------| gets |----------------| | -id: int | | -billNo: int | | -name: String | | -month: String | | -address | | -units: double | | -connectionNo | | -amount: double| |---------------| | -paid: boolean | | +getBills() | |----------------| | +makePayment( | | +calculate() | | bill, mode) | +----------------+ +---------------+ | 1 | * +------------------+ | Payment | |------------------| | -amount: double | | -date: Date | |------------------| | +process() | +------------------+ ^ ^ CashPayment ElectronicPayment -transactionId +process() ``` #### Mapping to code (Java) ```java import java.util.*; class Customer { private int id; private String name, address, connectionNo; private List bills = new ArrayList<>(); // 1 - * public Customer(int id, String name, String addr, String conn) { this.id = id; this.name = name; this.address = addr; this.connectionNo = conn; } public void addBill(Bill b) { bills.add(b); } public List getBills() { return bills; } public void makePayment(Bill bill, Payment p) { bill.addPayment(p); } } class Bill { private int billNo; private String month; private double units, amount; private boolean paid; private List payments = new ArrayList<>(); // 1 - * public Bill(int no, String month, double units) { this.billNo = no; this.month = month; this.units = units; this.amount = calculate(); } public double calculate() { return units * 25.0; } // assumed rate per unit public void addPayment(Payment p) { p.process(); payments.add(p); double paidSum = 0; for (Payment x : payments) paidSum += x.getAmount(); paid = paidSum >= amount; } public boolean isPaid() { return paid; } } abstract class Payment { protected double amount; protected Date date = new Date(); public Payment(double amount) { this.amount = amount; } public double getAmount() { return amount; } public abstract void process(); } class CashPayment extends Payment { public CashPayment(double a) { super(a); } public void process() { System.out.println("Cash received: " + amount); } } class ElectronicPayment extends Payment { private String transactionId; public ElectronicPayment(double a, String tid) { super(a); transactionId = tid; } public void process() { System.out.println("E-payment " + transactionId + ": " + amount); } } public class KuklApp { public static void main(String[] args) { Customer c = new Customer(1, "Hari", "Patan", "C-101"); Bill b = new Bill(1001, "Baisakh", 20); c.addBill(b); c.makePayment(b, new ElectronicPayment(500, "TX77")); System.out.println("Paid: " + b.isPaid()); } } ``` The one-to-many associations (multiplicity 1 to `*`) became `List` fields; generalization became `extends`; and the abstract `Payment.process()` is overridden in each subclass (polymorphism). The payment mode in `makePayment(bill, mode)` is represented by passing a `CashPayment` or `ElectronicPayment` object. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In the KUKL use case diagram, how is electronic payment related to Pay Bill? A. It extends Pay Bill as an optional choice of payment mode B. It replaces Login C. It is an actor D. It is a class attribute Answer: A. Pay Bill is extended by Pay Electronically, an optional payment mode, and the Payment Gateway is the external actor. (Key point: Extend relationship) 2. How is the 1-to-many association between Customer and Bill mapped to code? A. A single Bill field in Customer B. A List field in Customer C. A Customer field in a static method D. An integer count only Answer: B. The 'many' side is held as a collection, so Customer has List bills. (Key point: Multiplicity to collection) 3. How are CashPayment and ElectronicPayment related to Payment in the code? A. They are interfaces implemented by Payment B. They extend the abstract Payment class and override process() C. They contain Payment as a list D. They are unrelated Answer: B. Generalisation maps to extends, and the abstract process() is overridden in each subclass (polymorphism). (Key point: Generalization and polymorphism) 4. How does the code decide a Bill is paid? A. When any single payment is added B. When the sum of its payments is at least the bill amount C. When the customer logs in D. When units are greater than zero Answer: B. addPayment sums all payments and sets paid = paidSum >= amount. 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