AP Computer Science A Resource
Strings practice guide
A focused AP Computer Science A guide for String traversal, substring boundaries, comparison, and common string-building patterns.
Study Snapshot
AP unit
Units 1-2
Exam use
String APIs, loops, tracing, and FRQ helpers
Study time
35-45 min
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Best used when
Students who lose points on indexes, substring endpoints, equals vs ==, or loop boundaries.
String API Essentials
These methods appear constantly in AP-style tracing and implementation problems.
length() returns the number of characters.
charAt(index) returns one character at a zero-based index.
substring(start, end) includes start and excludes end.
indexOf(target) returns the first location or -1 when not found.
equals(other) compares content; == compares references.
String word = "computer";
System.out.println(word.length()); // 8
System.out.println(word.charAt(3)); // p
System.out.println(word.substring(1, 4)); // omp
System.out.println(word.indexOf("put")); // 3Traversal Patterns
Most String FRQ work is a careful loop with a small decision inside.
Count characters by scanning from 0 to length() - 1.
Build a new String when removing or replacing characters.
Use substring(i, i + 1) when the prompt expects String values instead of char values.
Check bounds before reading i + 1 or i - 1.
int count = 0;
for (int i = 0; i < word.length(); i++) {
if (word.charAt(i) == 'a') {
count++;
}
}FRQ Moves
AP questions reward small, predictable method-writing habits.
Name helper variables from the prompt so your logic is easy to read.
Return early only when it makes the method clearer.
Test empty strings, one-character strings, and strings with repeated characters.
After writing the loop, trace it once with a table of i, current character, and result.
Practice checklist
Use these prompts as a short self-check before moving back into FRQs or class assignments.
Related Practice
Keep practicing Strings from the right next page.
Use these links to move from the lesson into MCQ practice, FRQ writing, compiler drills, or a targeted tutoring plan.
For practice use only.
AP Computer Science A Strings Hard MCQ Practice
Practice hard AP Computer Science A String tracing, substring boundaries, indexOf reasoning, compareTo, equals versus ==, immutability, nested loops, and pattern detection.
Answered 0 of 25
Choose one answer.
After locating the first "ra", which substring is printed?
String s = "abracadabra";
int p = s.indexOf("ra");
System.out.print(s.substring(p, p + 4));Need help applying this?