AP Computer Science A Resource

ArrayList practice guide

A practical AP Computer Science A ArrayList guide covering add, get, set, remove, traversal, filtering, and common edge cases.

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Study Snapshot

AP unit

Unit 4

Exam use

Dynamic lists, removal loops, object collections, and FRQ data processing

Study time

45-60 min

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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 confuse arrays with ArrayLists or skip elements while removing items.

Use size(), not length

Use get/set instead of bracket access

Loop backward when removing multiple items

Core Methods

ArrayLists resize automatically and provide methods for common list operations.

add(value) appends to the end.

add(index, value) inserts and shifts later elements right.

get(index) reads an item.

set(index, value) replaces an item.

remove(index) removes and shifts later elements left.

ArrayList<Integer> nums = new ArrayList<Integer>();
nums.add(10);
nums.add(0, 5);
int first = nums.get(0);
nums.set(1, 12);

Traversal and Removal

Removal changes indexes immediately, so loop direction matters.

Use an indexed loop when you need positions.

Use an enhanced for loop only when you are not changing the list.

Loop backward when removing multiple matching elements.

Remember that remove shifts everything after the removed index.

for (int i = nums.size() - 1; i >= 0; i--) {
  if (nums.get(i) < 0) {
    nums.remove(i);
  }
}

Must-Know List Algorithms

These appear in MCQs and FRQs because they combine data access with control flow.

Find min or max by tracking the best value seen so far.

Filter into a new ArrayList when you should preserve the original list.

Swap two items using a temporary variable.

Remove duplicates by building a second list of values already seen.

Practice checklist

Use these prompts as a short self-check before moving back into FRQs or class assignments.

Remove all values below a threshold without skipping any elements.

Return a new ArrayList containing only words longer than five characters.

Swap the first and last elements of a list.

Find the object with the highest score in an ArrayList of objects.

For practice use only.

AP Computer Science A ArrayList Hard MCQ Practice

Practice hard AP Computer Science A ArrayList tracing, indexed add/remove shifts, forward and backward traversal, wrappers, aliasing, mutation, and common runtime errors.

Question 1 of 25

Answered 0 of 25

Choose one answer.

What is printed?

ArrayList<Integer> nums = new ArrayList<Integer>();
nums.add(2);
nums.add(4);
nums.add(6);
nums.add(1, 8);
nums.remove(2);
System.out.print(nums);

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