2021 AP CSA Free Response Questions | All Solutions & Scoring
2021 AP CSA Free Response Questions
Complete Java solutions, scoring rubrics, common mistakes, and exam tips for every 2021 AP CSA FRQ. All question text verified from the official College Board PDF.
The 2021 AP CSA FRQs
The 2021 exam followed the standard 4-question format. Each FRQ type appears in the same order every year, so you can prepare specifically for each position. Here are all four questions with direct links to full solutions.
WordMatch
Score word pairs by counting positional letter matches and total letter matches, implementing getWordScore() and scoreGuess() as two-part methods.
CombinedTable
Write a CombinedTable class representing two dining tables pushed together, computing capacity and desirability based on the component tables.
ClubMembers
Manage a club membership list: add members in sorted order, remove members by name, and find the nth member in a sorted ArrayList.
ArrayResizer
Determine if a 2D array row is non-zero, copy non-zero rows to build a resized array, and handle the case where all rows are zero.
Quick Reference: All Four 2021 FRQs
| FRQ | Problem | Type | Difficulty | Key Skill |
|---|---|---|---|---|
| FRQ 1 | WordMatch | Methods | Medium | String comparison via charAt(), positional vs total counting |
| FRQ 2 | CombinedTable | Class | Medium | Class composition, delegating to instance methods |
| FRQ 3 | ClubMembers | ArrayList | Medium-Hard | Sorted insertion position, remove() with object vs index |
| FRQ 4 | ArrayResizer | 2D Array | Hard | Row validation helper, building variable-size result array |
How Hard Were the 2021 AP CSA FRQs?
Overall: moderate-to-hard. FRQ 1 (WordMatch) tested String indexing and two distinct scoring modes, which required careful reading. Students who combined the two modes into one flawed method lost multiple rubric points.
FRQ 2 (CombinedTable) was a relatively clean class problem, but the capacity and desirability formulas depended on correctly calling methods on the component table objects. FRQ 3 and FRQ 4 both carried precision traps that cost points under time pressure.
FRQ 1: WordMatch — Medium
Two scoring modes: positional match (same index, same letter) and total match (letter appears anywhere). Students who conflated the two modes or used incorrect String methods lost points. charAt() and length() were essential.
FRQ 2: CombinedTable — Medium
Class composition: CombinedTable held two Table objects and computed combined capacity and desirability. The logic delegated to the component tables' methods. Well-structured OOP thinking made this straightforward.
FRQ 3: ClubMembers — Medium-Hard
Sorted insertion required finding the correct position before inserting. Removal by value used remove(Object), not remove(int) — a classic ArrayList overload trap. Both parts required precise index management.
FRQ 4: ArrayResizer — Hard
isNonZero() row helper was part (a); part (b) used it to build a new 2D array containing only non-zero rows. The hardest part: correctly sizing the result array after counting valid rows, and handling the all-zero edge case.
FRQ Type Pattern (Same Every Year Since 2019)
Since 2019, every AP CSA exam uses the same four question types in the same order. Knowing this pattern is a strategic advantage — you can rehearse your approach for each slot before exam day.
FRQ 1 — Methods & Control Structures
Write 1–2 methods using loops, conditionals, and expressions. Usually two parts: (a) implements helper logic, (b) calls (a) or extends it.
FRQ 2 — Class Writing
Write a complete class: instance variables, constructor, accessor/mutator methods, and at least one behavior method. Tests OOP design and encapsulation.
FRQ 3 — ArrayList Manipulation
Traverse, filter, modify, or build an ArrayList. Common traps: mutating while iterating, index drift after removals, and wrong method names.
FRQ 4 — 2D Array Operations
Navigate a 2D grid using nested loops. Tests row/column indexing, boundary awareness, and accumulation patterns. Often the most time-consuming question.
How to Use This Page
For best results: attempt each FRQ yourself first (set a 22-minute timer), then open the solution page and compare your code to the sample answer line by line. Pay special attention to the scoring rubric — you will often find you earned more points than you thought.
- Click any FRQ card above to open the full solution page.
- Each solution page includes the original question text, a complete Java solution, scoring rubric breakdown, and common mistakes to avoid.
- Use the FRQs by Topic page to find more practice on any specific concept.
- See all years at the FRQ Archive.
Frequently Asked Questions About the 2021 AP CSA FRQs
What are the 2021 AP CSA FRQs?
FRQ 1 WordMatch (Methods), FRQ 2 CombinedTable (Class Writing), FRQ 3 ClubMembers (ArrayList), FRQ 4 ArrayResizer (2D Array). Each worth 9 points, 36 total, 45% of the exam score.
What was the hardest 2021 FRQ?
FRQ 4 ArrayResizer was the most challenging. It required a row-validation helper method, then using that helper to selectively copy rows into a new 2D array of variable size. Handling the edge case where all rows are zero required careful null or empty array management.
What is the most common mistake on 2021 FRQ 3 ClubMembers?
Using remove(int index) when intending to remove by object, and finding the wrong insertion position for sorted order. Students who forgot that ArrayList.remove() is overloaded lost points by accidentally removing the wrong element.
How did 2021 compare in difficulty to other years?
The 2021 exam was moderately difficult and similar in structure to 2022. FRQ 1 required careful attention to the two scoring modes. FRQ 3 and FRQ 4 both had precision traps that separated well-prepared students from those relying on surface-level understanding.
Get in Touch
Whether you're a student, parent, or teacher — I'd love to hear from you.
Just want free AP CS resources?
Enter your email below and check the subscribe box — no message needed. Students get daily practice questions and study tips. Teachers get curriculum resources and teaching strategies.
Message Sent!
Thanks for reaching out. I'll get back to you within 24 hours.
Prefer email? Reach me directly at [email protected]