AP CSA 4.10 Exercise 2: Algorithms with ArrayLists Applied Practice

Unit 4: Data Collections · Lesson 4.10 · Exercise 2

Algorithms with ArrayLists: Applied Practice

Six scenarios on running the standard algorithms over a growable list, and what changes when the collection can shrink underneath the algorithm.

Back to the Lesson 4.10 pageAll Unit 4 lessons

How this one is different

These are the same algorithms as 4.5, so these six focus on what is genuinely different: size() rather than length, get() rather than brackets, and the fact that the collection can change.

Applied Practice

6 questions · scenario driven · every answer is recorded for your teacher

Question 1 of 6Apply
A max-finding algorithm is ported from an int array to an ArrayList.
Which change is required?
Incorrect. No conversion is needed to iterate and compare.
Incorrect. The algorithm is identical in structure; only the access syntax differs.
Correct. Correct. Recognizing that the ALGORITHM is the same is the point of the topic.
Incorrect. equals tests equality, not ordering. Autoboxing lets > work on the unboxed values.
Question 2 of 6Analyze
A method inserts a value into an ArrayList that is already sorted ascending, keeping it sorted.
What does the algorithm need to find first?
Incorrect. The maximum only matters if the new value exceeds it, which is one case of many.
Correct. Correct, and add(index, value) then shifts the rest right automatically.
Incorrect. The midpoint is only relevant to binary search, and even then it is a step rather than the answer.
Incorrect. Duplicates do not change where an insertion may legally go.
Question 3 of 6Apply
A method must count how many elements of an ArrayList have length greater than 5.
Which traversal is appropriate?
Correct. Correct. When you need only to read in order, the enhanced for is both shorter and immune to index errors.
Incorrect. That destroys the caller's list to answer a question that required no changes.
Incorrect. Nesting compares every pair, which is unrelated to counting.
Incorrect. Backward traversal solves a removal problem that this method does not have.
Question 4 of 6Analyze
A sum method over an ArrayList accumulates into an int.
What silently happens on each addition?
Incorrect. Concatenation happens only when one operand is a String.
Incorrect. No cast is involved; the conversion is defined by the language.
Incorrect. One is an object and one is a primitive. The conversion is real, just invisible.
Correct. Correct, and knowing it is happening explains why a null element throws NullPointerException here.
Question 5 of 6Evaluate
Two methods find the minimum of an ArrayList. One seeds with Integer.MAX_VALUE; the other seeds with list.get(0).
How do they differ on an empty list?
Incorrect. Neither returns null; one returns an int and the other does not return at all.
Incorrect. Neither produces 0 on empty input.
Correct. Correct. A wrong answer that looks valid is more dangerous than a crash, which is why an explicit empty check beats both.
Incorrect. Only the get(0) version throws; the other completes normally.
Question 6 of 6Apply
A program must find whether an ArrayList contains a given String value.
Which comparison is correct inside the loop?
Incorrect. == compares references, so it can report false for two equal strings held in different objects.
Correct. Correct. Object equality for Strings is always .equals.
Incorrect. Relational operators do not apply to String.
Incorrect. That is an assignment, and it does not compile in this position.

Where to go next

Try the Lesson 4.10 coding exercise Pick another Unit 4 lesson

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