Apex Class & Business Logic Practice Problems

Problem Statement

Create a utility class TemperatureConverter with two static methods:

• celsiusToFahrenheit(Decimal c) → returns Decimal
• fahrenheitToCelsius(Decimal f) → returns Decimal

Formulas: F = C × 9/5 + 32  |  C = (F − 32) × 5/9

Constraints

• Handle null input — return null if input is null
• Round to 2 decimal places

Problem Statement

Create a class OpportunityHelper with a static method isWon(String stage) that returns true if the stage equals "Closed Won" (case-insensitive), otherwise false.

Also add isLost(String stage) that returns true for "Closed Lost".

Problem Statement

Create a class StringUtils with these static methods:

• isPalindrome(String s) — returns true if s reads the same forwards and backwards (ignore case)
• countWords(String s) — returns the number of words (split on whitespace)
• capitalizeFirst(String s) — capitalizes the first letter of every word

Problem Statement

Create a class MathHelper with these static methods:

• factorial(Integer n) — returns n! (use recursion or iteration)
• isPrime(Integer n) — returns true if n is prime
• fibonacci(Integer n) — returns the nth Fibonacci number (0-indexed)

Constraints

• Handle n ≤ 0 gracefully (return 0 for fibonacci, 1 for factorial, false for isPrime)

Problem Statement

Create a class AccountService with:

• getHotAccounts() — returns a List<Account> where Rating = 'Hot', ordered by Name
• deactivateSmallAccounts(Decimal maxRevenue) — sets Active__c = false on all Accounts with AnnualRevenue < maxRevenue, updates them, returns the count updated

Problem Statement

Create a class DiscountCalculator with a static method getDiscountedPrice(Decimal originalPrice, Integer quantity):

• Quantity 1–9 → 0% discount
• Quantity 10–49 → 10% discount
• Quantity 50–99 → 20% discount
• Quantity ≥ 100 → 30% discount

Returns the final price per unit after discount, rounded to 2 decimal places.

Problem Statement

Create a class RecordTypeHelper with a static method:

getId(String objectName, String developerName)

Returns the Id of the RecordType matching the given sObject name and developer name, or null if not found.

Must cache results in a static Map so subsequent calls for the same object don't trigger more SOQL.

Problem Statement

Create a class JsonParser with a static method parseContacts(String jsonStr) that parses a JSON array of objects like:

[{"name":"Alice","email":"alice@x.com"},{"name":"Bob","email":"bob@x.com"}]

Returns a List<Contact> with LastName set from name and Email set from email.

Problem Statement

Create a class HttpCalloutService with a method callWithRetry(String endpoint, Integer maxRetries).

It should make an HTTP GET request, and if the response status is not 200, retry up to maxRetries times with a 1-second delay between attempts.

Return the response body on success, or throw a CalloutException after all retries are exhausted.

Problem Statement

Create a Batch Apex class DeactivateOldContactsBatch that:

• Implements Database.Batchable<SObject>
• Queries all Contacts where LastActivityDate < 365 days ago
• Sets Active__c = false on each Contact in the execute method
• Has a finish method that sends an email summary

Problem Statement

Create a class AccountValidator with a custom exception InvalidAccountException (extends Exception).

Add a static method validate(Account acc) that throws InvalidAccountException if:

• Account Name is blank
• AnnualRevenue is negative

Returns true if valid.

Problem Statement

Create a Queueable Apex class WelcomeEmailQueueable that:

• Implements Queueable
• Accepts a List<Id> of Contact IDs in its constructor
• In execute(): queries the contacts, sends a welcome email to each
• Enqueued with System.enqueueJob()

Problem Statement

Implement a selector class ContactSelector following enterprise patterns:

• getByIds(Set<Id> ids) — returns Contacts by ID with standard fields
• getByAccountId(Id accountId) — returns Contacts for an Account
• getByEmail(String email) — returns a Contact matching the email

All queries must select: Id, FirstName, LastName, Email, Phone, AccountId

Problem Statement

Write an Apex class LeadScorer with a static method calculateScore that computes a numeric lead score based on attributes.

Scoring rules:

• Industry: Technology = +30, Finance = +25, Healthcare = +20, other = +10
• Annual Revenue: >= 10,000,000 = +40, >= 1,000,000 = +25, >= 100,000 = +10, else 0
• Employee Count: >= 1000 = +20, >= 100 = +10, else 0
• Has Phone: +5 if phone is not null/blank
• Has Email: +5 if email is not null/blank

Maximum possible score: 100

Method Signature

static Integer calculateScore(String industry, Decimal annualRevenue, Integer employees, String phone, String email)

Constraints

• All parameters may be null — treat null numeric fields as 0
• Return an Integer score (0–100)

Problem Statement

Write an Apex class StageValidator with a static method isValidTransition that enforces allowed stage progressions for Opportunities.

Allowed transitions:

• Prospecting → Qualification, Closed Lost
• Qualification → Needs Analysis, Closed Lost
• Needs Analysis → Value Proposition, Closed Lost
• Value Proposition → Id. Decision Makers, Closed Lost
• Id. Decision Makers → Perception Analysis, Closed Lost
• Perception Analysis → Proposal/Price Quote, Closed Lost
• Proposal/Price Quote → Negotiation/Review, Closed Lost
• Negotiation/Review → Closed Won, Closed Lost
• Closed Won → (no transitions allowed)
• Closed Lost → (no transitions allowed)

Method Signature

static Boolean isValidTransition(String fromStage, String toStage)

Constraints

• Return true only for explicitly listed transitions
• Staying in the same stage returns false
• Null inputs return false

Problem Statement

Write an Apex class TerritoryMapper with a static method getRegion that maps US state codes to sales regions.

Region mappings:

• Northeast: ME, NH, VT, MA, RI, CT, NY, NJ, PA
• Southeast: DE, MD, VA, WV, NC, SC, GA, FL, AL, MS, TN, KY, AR, LA
• Midwest: OH, IN, IL, MI, WI, MN, IA, MO, ND, SD, NE, KS
• Southwest: TX, OK, NM, AZ
• West: CO, WY, MT, ID, WA, OR, CA, NV, UT, AK, HI
• Unknown state codes return 'Unknown'

Method Signature

static String getRegion(String stateCode)

Constraints

• State codes are uppercase 2-letter abbreviations
• Null or blank input returns 'Unknown'
• Case-insensitive matching (normalize to uppercase)

Problem Statement

Create an Apex REST service that exposes Account data via HTTP endpoints.

Requirements:

• Annotate the class with @RestResource(urlMapping='/accounts/*')
• Implement a GET method annotated with @HttpGet that queries Accounts and returns them as a JSON-serializable list
• Implement a POST method annotated with @HttpPost that accepts an Account name in the request body and inserts a new Account
• Implement a DELETE method annotated with @HttpDelete that deletes an Account by ID from the URL parameter
• Use RestContext.request and RestContext.response where needed
• Return appropriate HTTP status codes (200, 201, 400, 404)

Constraints

• All methods must be global static
• Handle the case where the record is not found (404)
• Use try/catch for DML operations

Problem Statement

Build a robust HTTP callout handler class and its corresponding mock for testing.

Requirements for HttpCalloutHandler:

• A method fetchExternalData(String endpoint) that makes an HTTP GET callout
• Parse the JSON response into a wrapper class ApiResponse with fields: Integer statusCode, String body, Boolean success
• If status code is 200, set success = true; otherwise false
• Handle callout exceptions — set success=false, statusCode=500, body=exception message

Requirements for HttpCalloutHandlerMock:

• Implement the HttpCalloutMock interface
• Implement the respond method returning a mock 200 response

Constraints

• Use Http, HttpRequest, HttpResponse classes
• Set request timeout to 10000ms (10 seconds)

Problem Statement

Design a robust custom exception hierarchy for a payment processing service.

Requirements:

• Create a base exception PaymentException extending Exception
• Create subclasses:
  • InsufficientFundsException — includes Decimal balance and Decimal required fields
  • InvalidCardException — includes String cardType field
  • PaymentGatewayException — includes Integer errorCode and String gatewayMessage
• Write a PaymentProcessor class with method processPayment(Decimal amount, String cardType, Decimal accountBalance)
• Throw InvalidCardException if cardType is not in ('Visa','Mastercard','Amex')
• Throw InsufficientFundsException if accountBalance < amount
• Otherwise return true

Constraints

• Each custom exception must extend the appropriate parent
• Custom fields must be set via constructor or setter before throwing

Problem Statement

Write an Apex class StringUtils with a static method reverseWords(String sentence) that reverses the order of words in a sentence while preserving each word's characters.

Examples

• "Hello World Apex" → "Apex World Hello"
• "I love Salesforce" → "Salesforce love I"
• null or blank → ""

Method Signature

public static String reverseWords(String sentence)

Problem Statement

Write an Apex class WordCounter with a static method countWords(List<String> words) that returns a Map<String, Integer> counting the frequency of each word (case-insensitive).

Examples

• ['apex','java','apex','APEX'] → {apex:3, java:1}
• Empty list → empty map

Method Signature

public static Map<String, Integer> countWords(List<String> words)

Problem Statement

Write an Apex class MathUtils with a static method factorial(Integer n) that returns n!.

Rules

• 0! = 1 and 1! = 1
• 5! = 120
• Return -1 for negative inputs

Method Signature

public static Integer factorial(Integer n)

Problem Statement

Write an Apex class FizzBuzz with a static method generate(Integer n) that returns a List<String> of 1 through n with:

• Multiples of 3 → "Fizz"
• Multiples of 5 → "Buzz"
• Multiples of both → "FizzBuzz"
• Otherwise → the number as a String

Method Signature

public static List<String> generate(Integer n)

Problem Statement

Your sales operations team needs to automatically classify accounts into revenue tiers to determine service level agreements and pricing models.

Write an Apex class AccountTierService with a static method getRevenueTier(Decimal annualRevenue) that returns a tier label based on the account's annual revenue.

Tier Definitions

Method Signature

public static String getRevenueTier(Decimal annualRevenue)

Best Practices

• Always handle null input gracefully — null revenue maps to 'Bronze'.
• Use a single return per branch for clarity.

Problem Statement

Your finance team requires that discount approvals are routed to the correct authority level based on the percentage discount being offered on an opportunity.

Write an Apex class DiscountApprovalService with a static method getApprovalLevel(Decimal discountPercent) that returns the required approver.

Approval Matrix

Method Signature

public static String getApprovalLevel(Decimal discountPercent)

Problem Statement

Your account management team needs a single numeric health score (0–100) per account to prioritise outreach. The score is calculated from five weighted factors.

Write an Apex class AccountHealthService with a static method getHealthScore(String industry, Decimal annualRevenue, String rating, Integer contactCount, String billingState) that returns an Integer score.

Scoring Factors

• Annual Revenue (0–30 pts): ≥ $1M = 30 | ≥ $500K = 20 | ≥ $100K = 10 | else 0
• Rating (0–25 pts): 'Hot' = 25 | 'Warm' = 15 | 'Cold' = 5 | else 0
• Industry (10–20 pts): 'Technology' or 'Finance' = 20 | else 10
• Contact Count (0–15 pts): ≥ 10 = 15 | ≥ 5 = 10 | ≥ 1 = 5 | else 0
• Billing State (0–10 pts): non-null/non-blank = 10 | else 0

Method Signature

public static Integer getHealthScore(String industry, Decimal annualRevenue, String rating, Integer contactCount, String billingState)

Problem Statement

Write an Apex class LeadQualifier with a static method qualify(String source, Integer numEmployees, Decimal budget) that returns a letter grade based on company size and budget.

Grading Rules

• A — employees ≥ 1,000 OR budget ≥ 500,000
• B — employees ≥ 200 OR budget ≥ 100,000
• C — employees ≥ 50
• Unqualified — everything else

Requirements

• Null-safe: treat null employees or budget as 0
• Define thresholds as named constants (not magic numbers)
• Use with sharing on the class

Problem Statement

Write an Apex class InvoiceCalculator with a static method calculateTotal(List<Decimal> lineItems, Decimal taxRate, Decimal discountPct) that computes the final invoice total.

Formula

subtotal     = sum of all positive line items
afterDiscount = subtotal × (1 − discountPct ÷ 100)
total         = afterDiscount × (1 + taxRate ÷ 100)
Return total rounded to 2 decimal places.

Requirements

• Skip null or negative line items
• Treat null taxRate or discountPct as 0
• Return 0 for null or empty line-item list
• Round the result to 2 decimal places using .setScale(2)

Problem Statement

Write an Apex class PhoneFormatter with a static method formatPhone(String rawPhone) that formats any 10-digit US phone number into the standard (XXX) XXX-XXXX pattern.

Rules

• Strip all non-digit characters first (dashes, dots, spaces, parens)
• If the result is exactly 10 digits, format as (XXX) XXX-XXXX
• If not 10 digits, return the original input unchanged
• If blank or null, return ""

Examples

• "415-555-1234" → "(415) 555-1234"
• "4155551234" → "(415) 555-1234"
• "415.555.1234" → "(415) 555-1234"
• "12345" → "12345" (not 10 digits)

Problem Statement

Write an Apex class SLAChecker with a static method isBreached(String priority, Integer hoursOpen) that returns true when a case has exceeded its SLA time limit.

SLA Thresholds

Requirements

• Return false for null/blank priority or null hoursOpen
• Return false for unknown priority values
• Store thresholds in a Map constant — no if-else chains

Problem Statement

Write an Apex class NameFormatter with two static methods:

Method 1 — fullName

public static String fullName(String salutation, String firstName, String lastName)

Concatenates non-blank parts separated by a single space.
e.g. fullName("Mr.", "John", "Smith") → "Mr. John Smith"
e.g. fullName(null, "John", "Smith") → "John Smith"

Method 2 — lastFirst

public static String lastFirst(String firstName, String lastName)

Returns "Last, First" format.
e.g. lastFirst("John", "Smith") → "Smith, John"
e.g. lastFirst(null, "Smith") → "Smith"

Requirements

• Skip blank/null parts — do not produce leading/trailing spaces
• Use String.isBlank() for null-safe blank checks

Problem Statement

Write a service class ContactMergeService with a static method mergeContactsByAccount(Id accountId) that merges duplicate Contacts under the same Account.

Two Contacts are duplicates when they share the same full name (case-insensitive). The oldest Contact (earliest CreatedDate) is kept as the master record.

Requirements

• public with sharing class.
• Throw IllegalArgumentException when accountId is null.
• Query Contacts ordered by CreatedDate ASC; group by full name (case-insensitive).
• Call Database.merge(master, List<Id>) with up to 2 IDs per call.
• System.debug the merged count — visible in the Output tab.
• Return the total number of merged records.

Problem Statement

Write AccountHealthScoreService with two static methods:

• calculateHealthScore(Id accountId) — single-account wrapper that System.debugs the score.
• calculateHealthScores(Set<Id> accountIds) — bulk-safe: exactly 4 SOQL queries total.

Scoring Rules (0–100, clamped)

• +40 — open Opportunity
• +30 — Closed Won in last 12 months
• +20 — LastActivityDate within 90 days
• −30 — open Case