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.

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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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Open FRQ Heat Map

Step 1StringsString APIs, loops, tracing, and FRQ helpers Step 2ArraysArray creation, indexing, traversal, mutation, algorithms, and 2D arrays Step 3ArrayListDynamic lists, removal loops, object collections, and FRQ data processing Step 4AlgorithmsSearch, sort, recursion, array/list processing, and runtime reasoning

Best used when

Students who lose points on indexes, substring endpoints, equals vs ==, or loop boundaries.

Use equals for content comparison

Trace substring end indexes carefully

Prefer charAt for single-character scans

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")); // 3

Traversal 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.

Write a method that counts how many times a target character appears in a word.

Write a method that returns a String with all spaces removed.

Write a method that determines whether a word is a palindrome.

Trace substring calls for start/end pairs before running code.

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.

Question 1 of 25

Answered 0 of 25

Choose one answer.

What is printed by the following code?

String s = "abracadabra";
int p = s.indexOf("ra");
System.out.print(s.substring(p, p + 4));

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