AP CSA Unit 4 Day 21: Array Copy Pitfall

February 6, 2026

Unit 4, Data Collections • Cycle 2

Day 21 Advanced Practice • Harder Difficulty

Focus: Array Copy Pitfall Hard Array Copy Pitfall

Advanced Practice Question

Format: Array Copy Pitfall

What is the output?

int[] a = {1, 2, 3};
int[] b = a;

b[0] = 99;

System.out.println(a[0]);

Difficulty: Hard | Topic: Array Copy Pitfall | Cycle: 2 (Advanced)

Why This Answer?

b = a makes b reference the SAME array as a (not a copy). Modifying b[0] also modifies a[0] because they point to the same array object.

Common Mistake

Watch Out!

Thinking = creates a copy of an array.

AP Exam Strategy

Array assignment copies the REFERENCE, not the array. Both variables point to same array.

This Cycle 2 HARD question tests array copy pitfall. Review Unit 4 concepts to build mastery of data collections.

Cycle 2 questions prepare you for the hardest AP CSA exam questions.