2004 AP CSA FRQ 1: WordList
Topic: ArrayList & String Processing
Skills Tested: ArrayList traversal, String length checking, removing while iterating
Curriculum Alignment: Unit 4 (Data Collections) (2025-2026 AP CSA)
Points: 9 | Time Estimate: ~22 minutes
Study This Topic: Unit 4: Data Collections Complete Study Guide
Part (a)
Write the numWordsOfLength method that returns the count of words with exactly len letters.
Try It First! Attempt to solve this part before viewing the solution. Use the concepts: ArrayList traversal.
Solution
public int numWordsOfLength(int len)
{
int numWords = 0;
for (int i = 0; i < myList.size(); i++)
{
String word = (String) myList.get(i);
if (word.length() == len)
numWords++;
}
return numWords;
}Part (b)
Write the removeWordsOfLength method that removes all words with exactly len letters from the list.
Solution
public void removeWordsOfLength(int len)
{
int i = 0;
while (i < myList.size())
{
String word = (String) myList.get(i);
if (word.length() == len)
myList.remove(i);
else
i++;
}
}Key Concepts
✓ Use a while loop (not for-each) when removing elements to avoid ConcurrentModificationException
✓ Only increment index when NOT removing an element
✓ Cast to String was required in 2004 (modern Java uses generics)
Common Mistakes to Avoid
✗ Using for-each loop when removing elements causes ConcurrentModificationException
✗ Incrementing index after removal causes skipped elements
✗ Off-by-one errors in loop bounds
✗ Forgetting to cast Object to String (2004 requirement)
Scoring Guidelines
Total Points: 9
Points are awarded for:
- Correct loop structure and bounds
- Proper method calls and return statements
- Correct conditional logic
- Handling edge cases appropriately
Partial credit is available for demonstrating understanding even with minor syntax errors.
Official College Board Resources
Continue Studying
About the Author: Tanner Crow is a certified AP Computer Science teacher with 11+ years of experience helping students succeed on the AP CSA exam.
Last updated: January 2026