What topics are on the AP CSA exam in 2026?

The 2025-2026 AP CSA exam covers four units: Unit 1 (Using Objects and Methods, ~15-25%), Unit 2 (Selection and Iteration, ~25-35%), Unit 3 (Arrays, ~10-18%), and Unit 4 (Data Collections including ArrayList and 2D Arrays, ~30-40%). The exam is 42 MCQ questions plus 4 FRQs, taken digitally via Bluebook.

What is the most important unit for the AP CSA exam?

Unit 4 (Data Collections) has the highest exam weight at 30-40% and appears most frequently in FRQs. Unit 2 (Selection and Iteration) is close behind at 25-35% and is essential for writing any working code. Both units should be prioritized in your study plan.

What String methods do I need to know for AP CSA?

The AP CSA Java Quick Reference provides: length(), substring(from, to), substring(from), indexOf(String), equals(String), and compareTo(String). Note that charAt() is NOT on the Quick Reference and should not be used. The most common mistake is forgetting that substring(from, to) excludes the character at the 'to' index.

What ArrayList methods do I need for AP CSA?

The AP CSA Quick Reference covers: size(), add(obj), add(index, obj), get(index), set(index, obj), and remove(index). The most common mistake is using .length instead of .size() on an ArrayList.

AP CSA Topics | AP Computer Science A Complete Topic List

AP Computer Science A Topics (2026) — Practice by Unit and Skill

Every AP CSA topic organized by the 2025–2026 four-unit curriculum: Using Objects and Methods, Selection and Iteration, Arrays, and Data Collections. Each topic page has code examples, hard practice questions, common mistake callouts, and exam tips. Built by Tanner Crow, AP CS teacher with 11+ years of experience and a 54.5% student rate of scoring 5s on the AP CSA exam.

Quick Navigation

AP CSA Exam Hub Unit 1 Study Guide Unit 2 Study Guide Unit 3 Study Guide Unit 4 Study Guide FRQ Archive 2026 Exam Info Common Mistakes

Unit 1 — Using Objects and Methods

▶ Exam Weight: ~15–25% | 8 Topic Pages | Focus: String methods, class anatomy, references, static vs. instance

String Methods

substring(), indexOf(), length(), compareTo(), equals() — with the exclusive-index trap

compareTo vs equals

When equals() returns boolean vs compareTo() returns int; the == reference trap

Object References and Aliasing

Heap storage, aliasing two variables to the same object, null reference crashes

Writing Classes

Private fields, constructors, methods, encapsulation — what AP graders expect

Constructors

No return type, parameter initialization, the void constructor mistake that costs FRQ points

Accessor and Mutator Methods

Getter/setter patterns, validation in mutators, aliasing risk with reference return types

Static vs Instance

One copy per class vs one per object; why static methods can't touch instance variables

Method Signatures and Return Types

void vs typed return, String immutability, discarding return values

Unit 2 — Selection and Iteration

▶ Exam Weight: ~25–35% | 12 Topic Pages | Focus: Booleans, loops, tracing, runtime errors — highest exam weight unit

Boolean Expressions and Logical Operators

&&, ||, !, operator precedence, De Morgan's Laws, I/II/III equivalence questions

Short-Circuit Evaluation

&& stops at first false; || stops at first true — null safety and divide-by-zero prevention

if/else Chains vs Independent ifs

Mutual exclusion, when independent ifs fire multiple branches unexpectedly

for Loop Tracing and Off-by-One Errors

Loop anatomy, < vs <=, step-by-step trace, counting iterations exactly

while Loops and Sentinel Loops

When to use while vs for, sentinel value pattern, infinite loop causes

Nested Loops

Total iterations = outer × inner (NOT outer + inner); grid and triangle patterns

String Traversal Patterns

substring(i, i+1) to get one character — charAt() is NOT on the Quick Reference

Common Loop Bugs

Infinite loops, skipping last element, double-increment, wrong update expression

break and continue

break exits innermost loop only; continue skips to next iteration — nested loop traps

Accumulators, Counters, Max and Min

Running sum, find max initialized to arr[0] not 0, linear search returning index or -1

Validating Input and Guard Conditions

Null checks, bounds checks, defensive programming — what FRQ graders deduct for

Runtime Errors: NullPointerException and ArrayIndexOutOfBoundsException

What triggers each, how to prevent, reading a stack trace concept

Unit 3 — Arrays

▶ Exam Weight: ~10–18% | 8 Topic Pages | Focus: Array creation, traversal, classic algorithms, arrays of objects

Array Initialization and Default Values

int[] default is 0; object[] default is null; arr.length has no parentheses

Array Traversal: Standard vs Enhanced for Loop

Standard for allows modification; enhanced for-each is read-only — assigning to loop variable does nothing

Finding Max, Min, and Counting in Arrays

Initialize max to arr[0] not 0 — breaks for all-negative arrays otherwise

Adjacent Element Patterns: i and i+1

Loop must stop at length-2 when accessing i+1; sorted-order checking pattern

Shifting Elements in Arrays

Shift right to insert (work backward); shift left to delete (work forward) — direction matters

Parallel Arrays

Keeping two arrays in sync; the bug when you sort one without the other

ArrayIndexOutOfBoundsException

Four ways to cause it; last valid index is arr.length-1 — high-search standalone page

Arrays of Objects

new Dog[5] gives 5 null references, NOT 5 Dog objects — must construct each element

Unit 4 — Data Collections

▶ Exam Weight: ~30–40% | 10 Topic Pages | Focus: ArrayList, 2D Arrays, searching, sorting — most heavily tested in FRQs

ArrayList Basics

add(), get(), set(), remove(), size() — size() not length; wrapper types required

ArrayList Traversal

Standard for with size(), enhanced for-each (read only), backward traversal for safe removal

Removing from ArrayList While Iterating

Forward remove skips elements; backward iteration or index-decrement fix

Sorting an ArrayList

Collections.sort(), Comparable interface concept, sorting objects by field

ArrayList of Objects

get() returns reference — calling mutator on returned reference DOES modify the list object

2D Arrays: Basics and Row-Major Traversal

grid[row][col]; grid.length = rows; grid[0].length = cols; nested loop traversal

2D Array Column-Major and Diagonal Patterns

Column-major traversal, main diagonal (row==col), anti-diagonal, row/column sums

2D Array Neighbor Checks and Bounds

Safe up/down/left/right neighbor access with full bounds check before every access

Searching and Sorting

Linear search O(n), binary search O(log n) on sorted only, selection sort, insertion sort

Pass-by-Value in Java

Primitives unchanged after method call; object fields CAN change; reassigning parameter has no effect

Standard Algorithms and Patterns

These patterns appear across multiple units and recur heavily in both MCQ and FRQ. Master the pattern, not just the syntax.

Accumulators, Counters, Max/Min

Running sum and count; initialize max to first element, not zero

Linear Search in Arrays

Scan and return index; return -1 if not found; use boolean flag for found/not-found

Adjacent Element Comparison

i and i+1 loop pattern; loop to length-2; sorted-order detection

Selection Sort and Insertion Sort

Selection: find min, swap; insertion: shift and place; binary search requires sorted input

FRQ Skills and Scoring Patterns

AP CSA has 4 FRQs worth 45% of the exam score. Each FRQ tests specific coding skills. Practice the released FRQs below — solutions include scoring rubric breakdowns and common point-loss patterns.

FRQ Archive 2025 FRQ 1 — DogWalker 2025 FRQ 2 — SignedText 2025 FRQ 3 — Round 2025 FRQ 4 — SumOrSameGame 2018 FRQ 1 — FrogSimulation

Common Mistakes That Cost Points

Every topic page has a dedicated Common Mistake box. The full aggregated list — 20+ specific errors organized by unit, each with a code example — is on the dedicated mistakes page. Teachers bookmark and share it.

→ See All AP CSA Common Mistakes (2026)

Quick Reference — String and ArrayList Methods

These are the only String and ArrayList methods provided on the AP CSA Java Quick Reference sheet. If a method is NOT in this table, you cannot assume it exists on the exam.

Method	Return Type	What It Does
`int length()`	int	Number of characters in the String
`String substring(int from, int to)`	String	Characters from index from up to (NOT including) to
`String substring(int from)`	String	Characters from index from to the end
`int indexOf(String s)`	int	Index of first occurrence; -1 if not found
`boolean equals(String other)`	boolean	True if same character sequence (use instead of ==)
`int compareTo(String other)`	int	Negative if before, 0 if equal, positive if after (lexicographic)

ArrayList Method	Return Type	What It Does
`int size()`	int	Number of elements (NOT .length — that is an array field)
`boolean add(E obj)`	boolean	Appends obj to end; always returns true
`void add(int index, E obj)`	void	Inserts obj at index; shifts elements right
`E get(int index)`	E	Returns element at index (does NOT remove it)
`E set(int index, E obj)`	E	Replaces element at index with obj; returns old element
`E remove(int index)`	E	Removes and returns element at index; shifts elements left

Bonus: Error-Specific Reference Pages

These pages target the exact error messages students search for. Each has 4–6 code examples showing every way to cause and fix the error.

NullPointerException

All the ways null causes a crash; null checks; array of objects all null by default

ArrayIndexOutOfBoundsException

arr.length vs arr.length-1; the i+1 pattern; off-by-one crash scenarios

AP CSA Exam Hub FRQ Archive 2026 Exam Info Common Mistakes

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