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AP CSA Unit-Level MCQ

ArrayList Traversal

Practice mode with 15 Java-focused questions, immediate answer checks, and explanations.

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What arraylist traversal covers

Traversing an ArrayList uses either an index from 0 while it is less than size(), or an enhanced for loop over the elements. The indexed form is required whenever you need the position or plan to call set. The enhanced form is cleaner for read-only work such as summing, counting, or finding a maximum, but structurally modifying the list while an enhanced for loop is running is unsafe.

Where students lose points

Calling size() once and caching it, then adding or removing inside the loop, produces stale bounds. Students also mix the two loop styles in one traversal, and they use get(i) with a bound of <= size(), which throws an IndexOutOfBoundsException.

How it shows up on the AP exam

Unit 4 content that combines with accumulator patterns from Unit 2. Most ArrayList FRQ parts are a traversal with one decision inside it.

For practice use only.

ArrayList Traversal MCQ Practice

AP CSA ArrayList traversal practice: indexed and enhanced for loops over lists, accumulating results, and avoiding modification during iteration.

Question 1 of 15

Answered 0 of 15

Choose one answer.

Code Tracing 01 - ArrayList Traversal: track the final printed value.

import java.util.ArrayList;
public class Main {
  public static void main(String[] args) {
    ArrayList<Integer> nums = new ArrayList<Integer>();
    nums.add(3);
    nums.add(7);
    nums.add(3);
    nums.add(9);
    nums.add(5);
    int total = 0;
    for (int i = 0; i < nums.size(); i += 2) {
      total += nums.get(i);
    }
    System.out.print(total);
  }
}

All 15 arraylist traversal questions

Work through the interactive quiz above first. This is the full arraylist traversal question set with worked solutions, so students can review any question after attempting it.

  1. 1.Code Tracing 01 - ArrayList Traversal: track the final printed value.

    import java.util.ArrayList;
public class Main {
  public static void main(String[] args) {
    ArrayList<Integer> nums = new ArrayList<Integer>();
    nums.add(3);
    nums.add(7);
    nums.add(3);
    nums.add(9);
    nums.add(5);
    int total = 0;
    for (int i = 0; i < nums.size(); i += 2) {
      total += nums.get(i);
    }
    System.out.print(total);
  }
}
    • 11
    • 27
    • 18
    • 3
    Show worked solution

    Correct answer: 11

    Stepping the index by 2 visits only the even positions of the list.

  2. 2.Code Tracing 12 - ArrayList Traversal: follow the variable updates.

    import java.util.ArrayList;
public class Main {
  public static void main(String[] args) {
    ArrayList<Integer> nums = new ArrayList<Integer>();
    nums.add(5);
    nums.add(9);
    nums.add(5);
    nums.add(11);
    nums.add(7);
    int total = 0;
    for (int v : nums) {
      total += v;
    }
    System.out.print(total);
  }
}
    • 7
    • 37
    • 5
    • 32
    Show worked solution

    Correct answer: 37

    The enhanced for loop reads every element in order, and each Integer is automatically unboxed into the int accumulator.

  3. 3.Code Tracing 28 - ArrayList Traversal: trace the branch and loop path.

    import java.util.ArrayList;
public class Main {
  public static void main(String[] args) {
    ArrayList<Integer> nums = new ArrayList<Integer>();
    nums.add(8);
    nums.add(8);
    nums.add(3);
    nums.add(11);
    nums.add(10);
    for (int i = 0; i < nums.size(); i++) {
      if (nums.get(i) % 2 == 0) nums.remove(i);
    }
    System.out.print(nums);
  }
}
    • [8, 8, 10]
    • [8, 3, 11]
    • [3, 11]
    • [8, 8, 3, 11, 10]
    Show worked solution

    Correct answer: [8, 3, 11]

    Removing while moving forward shifts the next element into the current index, so the loop skips past it.

  4. 4.Code Tracing 39 - ArrayList Traversal: watch the index changes.

    import java.util.ArrayList;
public class Main {
  public static void main(String[] args) {
    ArrayList<Integer> nums = new ArrayList<Integer>();
    nums.add(10);
    nums.add(10);
    nums.add(5);
    nums.add(10);
    nums.add(6);
    for (int i = nums.size() - 1; i >= 0; i--) {
      if (nums.get(i) % 2 == 0) nums.remove(i);
    }
    System.out.print(nums);
  }
}
    • [10, 10, 10, 6]
    • The code does not compile.
    • [5]
    • [10, 10, 5, 10, 6]
    Show worked solution

    Correct answer: [5]

    Walking backwards means a removal only shifts elements the loop has already passed, so nothing gets skipped.

  5. 5.Code Tracing 50 - ArrayList Traversal: evaluate the state change step by step.

    import java.util.ArrayList;
public class Main {
  public static void main(String[] args) {
    ArrayList<Integer> nums = new ArrayList<Integer>();
    nums.add(12);
    nums.add(8);
    nums.add(7);
    nums.add(9);
    nums.add(8);
    for (int v : nums) {
      if (v == 8) nums.remove(Integer.valueOf(v));
    }
    System.out.print(nums);
  }
}
    • [12, 7, 9]
    • [12, 8, 7, 9, 8]
    • (no output)
    • A runtime exception is thrown.
    Show worked solution

    Correct answer: A runtime exception is thrown.

    Structurally changing a list while an enhanced for loop is iterating it throws ConcurrentModificationException.

  6. 6.What is printed by the following code segment?

    ArrayList<Integer> l = new ArrayList<Integer>();
for (int i = 1; i <= 4; i++) { l.add(i * i); }
int s = 0;
for (int i = 1; i < l.size(); i++)
{
    s += l.get(i) - l.get(i - 1);
}
System.out.print(s);
    • 15
    • 30
    • 10
    • 16
    Show worked solution

    Correct answer: 15

    Consecutive differences telescope, so the total equals the last element minus the first.

  7. 7.What is printed by the following code segment?

    ArrayList<String> l = new ArrayList<String>();
l.add("aa");
l.add("b");
l.add("ccc");
String out = "";
for (String v : l)
{
    out = v.length() > out.length() ? v : out;
}
System.out.print(out);
    • aa
    • ccc
    • b
    • aabccc
    Show worked solution

    Correct answer: ccc

    The conditional keeps whichever string is longer as the traversal proceeds.

  8. 8.What is printed by the following code segment?

    ArrayList<Integer> l = new ArrayList<Integer>();
l.add(4);
l.add(8);
l.add(2);
for (int i = 0; i < l.size(); i++)
{
    l.set(i, l.get(i) / 2);
}
System.out.print(l);
    • [4, 8, 2]
    • [2, 4, 2]
    • [2, 4, 1]
    • [8, 16, 4]
    Show worked solution

    Correct answer: [2, 4, 1]

    Calling set replaces each element in place without changing the size.

  9. 9.What is printed by the following code segment?

    ArrayList<Integer> l = new ArrayList<Integer>();
l.add(1);
l.add(2);
l.add(3);
String out = "";
for (int i = l.size() - 1; i >= 0; i--)
{
    out += l.get(i);
}
System.out.print(out);
    • 123
    • 3
    • 1
    • 321
    Show worked solution

    Correct answer: 321

    An indexed loop can run backward, which the enhanced form cannot do.

  10. 10.What is printed by the following code segment?

    ArrayList<Integer> l = new ArrayList<Integer>();
l.add(5);
l.add(3);
l.add(9);
l.add(1);
int idx = 0;
for (int i = 1; i < l.size(); i++)
{
    if (l.get(i) < l.get(idx)) { idx = i; }
}
System.out.print(idx + " " + l.get(idx));
    • 3 1
    • 1 3
    • 2 9
    • 0 5
    Show worked solution

    Correct answer: 3 1

    The loop tracks the position of the smallest element rather than the value.

  11. 11.What is printed by the following code segment?

    ArrayList<String> l = new ArrayList<String>();
l.add("cat");
l.add("cow");
l.add("dog");
int c = 0;
for (String v : l)
{
    if (v.charAt(0) == 'c') { c++; }
}
System.out.print(c);
    • 3
    • 2
    • 1
    • 0
    Show worked solution

    Correct answer: 2

    Comparing a char with == is correct, and two elements start with the letter c.

  12. 12.What is printed by the following code segment?

    ArrayList<Integer> a = new ArrayList<Integer>();
a.add(1);
a.add(2);
ArrayList<Integer> b = new ArrayList<Integer>();
for (int v : a) { b.add(v * 10); }
b.add(99);
System.out.print(a.size() + " " + b.size());
    • 3 3
    • 2 2
    • 2 3
    • 3 2
    Show worked solution

    Correct answer: 2 3

    Building a second list leaves the first untouched, so only the copy grows.

  13. 13.What is printed by the following code segment?

    ArrayList<Integer> l = new ArrayList<Integer>();
for (int i = 1; i <= 6; i++) { l.add(i); }
int s = 0;
for (int i = 1; i < l.size(); i += 2)
{
    s += l.get(i);
}
System.out.print(s);
    • 9
    • 21
    • 6
    • 12
    Show worked solution

    Correct answer: 12

    Stepping by two from index 1 collects the elements 2, 4, and 6.

  14. 14.What is printed by the following code segment?

    ArrayList<Integer> l = new ArrayList<Integer>();
l.add(2);
l.add(2);
l.add(5);
int runs = 1;
for (int i = 1; i < l.size(); i++)
{
    if (!l.get(i).equals(l.get(i - 1))) { runs++; }
}
System.out.print(runs);
    • 2
    • 3
    • 1
    • 5
    Show worked solution

    Correct answer: 2

    Using equals rather than == is essential because the elements are Integer objects.

  15. 15.What is printed by the following code segment?

    ArrayList<Integer> l = new ArrayList<Integer>();
int s = 0;
for (int v : l) { s += v; }
System.out.print(l.size() + " " + s + " " + l.isEmpty());
    • 0 0 false
    • 0 0 true
    • An exception is thrown.
    • 0 null true
    Show worked solution

    Correct answer: 0 0 true

    Traversing an empty list simply never enters the body.