How to use this page: For each problem, read the code, trace through it on paper, write your predicted output, then check the solution. Do not skip the trace — that is the skill the exam tests.
Problem 1
Accumulator With Conditional
What is printed when the following code executes?
int[] vals = {3, 7, 2, 8, 5, 1};
int result = 0;
for (int i = 0; i < vals.length; i++)
{
if (vals[i] > 4)
{
result += vals[i];
}
}
System.out.println(result);
Answer: 20
Only values greater than 4 are added: 7 + 8 + 5 = 20. Values 3, 2, and 1 are skipped by the condition.
Only values greater than 4 are added: 7 + 8 + 5 = 20. Values 3, 2, and 1 are skipped by the condition.
Problem 2
In-Place Modification
What does the array contain after this code executes?
int[] data = {10, 20, 30, 40, 50};
for (int i = 0; i < data.length - 1; i++)
{
data[i] = data[i + 1];
}
// What is data now?
Answer: {20, 30, 40, 50, 50}
Each element is replaced by the one to its right. The last element (50) is never overwritten because the loop stops at
Each element is replaced by the one to its right. The last element (50) is never overwritten because the loop stops at
length - 1. This is a left-shift pattern.Problem 3
Swap Adjacent Pairs
What does the array contain after execution?
int[] arr = {1, 2, 3, 4, 5, 6};
for (int i = 0; i < arr.length - 1; i += 2)
{
int temp = arr[i];
arr[i] = arr[i + 1];
arr[i + 1] = temp;
}
// What is arr now?
Answer: {2, 1, 4, 3, 6, 5}
The loop increments by 2, swapping pairs: (1,2) becomes (2,1), (3,4) becomes (4,3), (5,6) becomes (6,5).
The loop increments by 2, swapping pairs: (1,2) becomes (2,1), (3,4) becomes (4,3), (5,6) becomes (6,5).
Problem 4
Nested Condition With Count
What is printed?
int[] scores = {85, 92, 78, 95, 88, 76, 91};
int count = 0;
for (int k = 0; k < scores.length; k++)
{
if (scores[k] >= 90)
{
count++;
}
}
System.out.println(count);
Answer: 3
Values >= 90: 92, 95, 91. Three elements meet the condition.
Values >= 90: 92, 95, 91. Three elements meet the condition.
Problem 5
Reverse Traversal With String Building
What is printed?
String[] letters = {"A", "B", "C", "D"};
String result = "";
for (int i = letters.length - 1; i >= 0; i--)
{
result += letters[i];
}
System.out.println(result);
Answer: DCBA
The loop starts at the last index (3) and decrements to 0, concatenating each element in reverse order.
The loop starts at the last index (3) and decrements to 0, concatenating each element in reverse order.
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Aliasing Trace
What is printed?
int[] x = {5, 10, 15};
int[] y = x;
y[1] = 99;
System.out.println(x[1]);
Answer: 99
y = x makes both variables point to the same array. Changing y[1] also changes x[1]. This is aliasing.Problem 7
Find Index of Minimum
What is printed?
int[] nums = {14, 7, 23, 3, 18};
int minIdx = 0;
for (int i = 1; i < nums.length; i++)
{
if (nums[i] < nums[minIdx])
{
minIdx = i;
}
}
System.out.println(minIdx + " " + nums[minIdx]);
Answer: 3 3
The minimum value is 3 at index 3. The loop finds the index, not the value — a common exam distinction.
The minimum value is 3 at index 3. The loop finds the index, not the value — a common exam distinction.