1Z0-829 Controlling Program Flow Practice Test 6 — 15 Questions

Question 1

What is the output of the following code? int i=5; do { System.out.print(i); i--; } while(i>0);

Accepted Answer

54321. The do-while loop executes the body first, printing the current value of i (5), then decrements i to 4. The loop continues while i > 0, so it prints 5, 4, 3, 2, 1, and stops when i becomes 0, as the condition i > 0 is false. This results in the output "54321".

Answer

Compilation error

Answer

543210

Answer

5432

Question 2

A developer wrote a method that uses a for-each loop to iterate over a list of strings and remove elements that match a certain condition. However, the method throws a ConcurrentModificationException at runtime. What is the most likely cause?

Accepted Answer

The loop modifies the list by calling remove() on the list itself.. A for-each loop internally uses an Iterator to traverse the list. If the list is structurally modified (e.g., by calling remove() directly on the list) during iteration, the iterator's expected modCount will differ from the actual modCount, triggering a ConcurrentModificationException. This is a fail-fast behavior of the ArrayList and other Collection implementations.

Answer

The loop uses a for-each loop with an array instead of a list.

Answer

The loop uses an iterator that is not properly initialized.

Answer

The list is unmodifiable.

Question 3

A junior developer writes a method that uses a switch statement to handle different types of user input. The input is an integer representing an operation code. The developer uses a traditional switch statement with break statements. However, when operation code 2 is entered, the program also executes the code for operation 3. What is the most likely cause?

Accepted Answer

The break statement is missing after the operation 2 case.. In a traditional Java switch statement, execution continues into the next case block unless a break statement is encountered. If operation code 2 executes the code for operation 3, it indicates that the break statement is missing after the case for operation 2, causing fall-through to the next case.

Answer

The operation codes are not mutually exclusive.

Answer

The variable is being modified inside the switch.

Answer

The switch statement uses fall-through by design.

Question 4

A developer is implementing a batch processing application that reads records from a list and processes them. The method uses a for loop with an index variable. Inside the loop, if a record is null, the developer wants to skip that iteration and continue with the next index. The developer writes: for (int i = 0; i < records.size(); i++) { if (records.get(i) == null) continue; process(records.get(i)); updateCounter(); } However, the counter is not updated correctly. The developer expects the counter to reflect the number of processed (non-null) records. What is the problem?

Accepted Answer

The continue statement skips the rest of the loop body, including the counter update.. The `continue` statement immediately jumps to the next iteration of the loop, skipping any remaining code in the current iteration. In this case, `updateCounter()` is placed after the `continue` in the loop body, so when a null record is encountered, the counter update is never executed, causing the counter to not reflect the number of processed (non-null) records.

Answer

The continue statement is only valid inside a while loop.

Answer

The continue statement should be replaced with a break.

Answer

The counter variable should be declared as volatile.

Question 5

A developer needs to iterate over a List<String> and remove elements that are null. Which approach guarantees correct behavior without throwing a ConcurrentModificationException?

Accepted Answer

Use an Iterator explicitly and call its remove() method. Iterator.remove() is the safe and recommended way to remove elements during iteration, avoiding ConcurrentModificationException. Option A is incorrect because using list.remove() inside a for-each loop modifies the list directly while iterating, causing ConcurrentModificationException. Option B is incorrect because Stream.filter() does not modify the original list; it creates a new list, which may not meet the requirement to remove elements from the original. Option C is incorrect because although a decrementing for loop may work, it is error-prone and not the guaranteed approach; it is not the idiomatic Java solution.

Answer

Use a for-each loop and call list.remove() on the current element

Answer

Use a Stream's filter() method and collect the results

Answer

Use a traditional for loop with an index that decrements

Question 6

Given an enum Direction { NORTH, SOUTH, EAST, WEST } and a variable d of type Direction, which code snippet correctly uses a switch expression to map each direction to an abbreviation (N, S, E, W) without using a default branch?

Accepted Answer

switch (d) { case NORTH -> "N"; case SOUTH -> "S"; case EAST -> "E"; case WEST -> "W"; }. It uses the arrow syntax in a switch expression, which requires that all possible enum values are covered without a default branch. Since Direction has exactly four constants and each is mapped to a yield value via the arrow, the switch is exhaustive and compiles successfully.

Answer

switch (d) { case NORTH: yield "N"; case SOUTH: yield "S"; case EAST: yield "E"; case WEST: yield "W"; }

Answer

switch (d) { case NORTH -> "N"; case SOUTH -> "S"; case EAST -> "E"; }

Answer

switch (d) { case NORTH: yield "N"; case SOUTH: yield "S"; case EAST: yield "E"; default: yield "W"; }

Question 7

Which two statements about the enhanced for-each loop in Java are true? (Choose two.)

Accepted Answer

It requires the target to implement the Iterable interface, except for arrays.. The enhanced for-each loop requires the target to implement the Iterable interface, except for arrays, which are handled natively by the compiler using index-based iteration. This is specified in the Java Language Specification (JLS §14.14.2), where arrays are a special case that does not require Iterable.

Answer

It can safely modify the underlying collection during iteration.

Answer

It can be used to iterate directly over a Stream object.

Answer

It provides an implicit counter variable that can be accessed.

Question 8

Refer to the exhibit. What is the output when the program is executed?

Accepted Answer

0 0 0 1 0 2 1 0 1 1. The code uses nested for loops with break labels. The outer loop iterates i from 0 to 2, and the inner loop iterates j from 0 to 2. When i == 1 and j == 1, the break outer; statement exits both loops, so after printing 0 0, 0 1, 0 2, 1 0, 1 1, the program terminates. This matches option C.

Answer

0 0 0 1 0 2 1 0 1 1 1 2

Answer

0 0 0 1 0 2 1 0 1 1 2 0 2 1 2 2

Answer

0 0 0 1 0 2 1 0 1 1 1 2 2 0 2 1 2 2

Question 9

A developer is writing a utility to validate user input. The method receives an integer `score` and must assign a letter grade based on the following rules:

- If `score` is 90 or above, grade is 'A'.
- If `score` is between 80 and 89 (inclusive), grade is 'B'.
- If `score` is between 70 and 79 (inclusive), grade is 'C'.
- Otherwise, grade is 'F'.

They implement the logic using a traditional switch statement, but the code fails to compile. Which of the following is the most likely cause of the compilation error?

Accepted Answer

The case labels use relational operators (e.g., `case score >= 90:`).. The compilation error occurs because traditional switch statements require case labels to be constant expressions, such as literals or final variables. Relational expressions like `score >= 90` are not constant and cannot be used as case labels. To implement range-based grading, an if-else chain is appropriate, or a switch expression with pattern matching (if using preview features). The other options do not cause this specific error.

Answer

The switch statement is missing a break statement after each case.

Answer

The switch statement is missing a default case.

Answer

The switch statement uses a boolean expression as its selector.

Question 10

A payroll application must classify each employee's weekly hours into a pay band. The developer writes: ```java int hours = 44; String band = switch (hours) { case 0, 1, 2 -> "NONE"; default -> { if (hours <= 40) yield "STANDARD"; else if (hours <= 50) yield "OVERTIME"; else yield "EXCESSIVE"; } }; System.out.println(band); ``` What is printed?

Accepted Answer

OVERTIME. A switch expression must produce a value on every path, and the default arm here is a block that uses yield to return a result. With hours equal to 44, no constant label matches, so the default block executes; its first condition fails and the second succeeds, yielding OVERTIME. The arrow-form block with yield is the key construct being exercised.

Answer

A compile-time error, because a switch expression cannot use default together with constant case labels.

Answer

EXCESSIVE

Answer

STANDARD

Question 11

A telemetry service receives sensor readings and must stop consuming as soon as a reading exceeds a threshold, while also skipping readings flagged as invalid. The developer writes:

```java
int[] readings = {5, 30, 12, -1, 60, 8};
int total = 0; int processed = 0;
for (int r : readings) {
    if (r < 0) continue;
    if (r > 50) break;
    total += r;
    processed++;
}
System.out.println(total + ":" + processed);
```
What is printed?

Accepted Answer

47:3. In an enhanced for loop, continue abandons the current element and moves to the next, while break exits the entire loop. The negative reading is discarded, the values 5, 30, and 12 accumulate to 47 and increment the counter three times, and the reading of 60 halts iteration before it can be added or counted.

Answer

107:4

Answer

42:3

Answer

47:4

Question 12

A developer is using a nested loop to process a 4x4 grid. They want to skip the remaining iterations of the inner loop whenever the column index equals the row index, but continue with the next row. Which control flow statement should be placed inside the inner loop to achieve this?

Accepted Answer

continue;. The continue statement is designed to skip the current iteration of the innermost loop and proceed to the next iteration. In a nested loop, placing continue inside the inner loop when a condition is met (such as column equals row) will skip the rest of that inner loop's body for that specific iteration, then continue with the next column. This matches the requirement to skip the diagonal element while still processing other columns and moving to the next row.

Answer

break outer;

Answer

return;

Answer

break;

Question 13

A developer writes a while loop to print numbers from 1 to 5. The loop condition is while (count <= 5). Inside the loop, they increment count after printing. What is the output?

Accepted Answer

1 2 3 4 5. With count initialized to 1 and the condition count <= 5, the loop prints the value of count and then increments it. The sequence of printed values is 1, 2, 3, 4, 5. After printing 5, count becomes 6, and the loop condition fails, so the loop terminates. Thus, the output is the numbers 1 through 5.

Answer

1 2 3 4 5 6

Answer

0 1 2 3 4 5

Answer

1 2 3 4

Question 14

A developer writes a method that must label each processed parcel with a route code derived from its weight bracket. The code is:

```java
int bracket = 3;
String route = switch (bracket) {
    case 1 -> "LOCAL";
    case 2, 3 -> "REGIONAL";
    default -> "NATIONAL";
};
System.out.println(route);
```

What is printed?

Accepted Answer

REGIONAL. A switch expression with arrow labels performs strict constant matching against the selector; the first matching label wins and no fall-through exists. Because the grouped label lists both 2 and 3, the selector value 3 selects the arm yielding REGIONAL. Grouping constants in one label is legal and is the idiomatic way to share a single result across several values.

Answer

LOCAL

Answer

NATIONAL

Answer

Compilation fails because two constants appear in a single case label.

Question 15

A developer writes the following method to print a countdown for a rocket launch:

```java
public static void countdown() {
    for (int i = 5; i > 0; i--) {
        if (i == 3) {
            continue;
        }
        System.out.print(i + " ");
    }
    System.out.print("Liftoff");
}
```

What is printed when countdown() is invoked?

Accepted Answer

5 4 2 1 Liftoff. The continue statement abandons the remainder of the current iteration and moves to the update expression, so the value 3 is never printed while 5, 4, 2, and 1 are. After the loop ends, the trailing print statement executes normally, appending 'Liftoff'. The result is the countdown with the single skipped value followed by the final message.

Answer

5 4 2 1 Liftoff, then the loop repeats

Answer

5 4 2 1

Answer

5 4 3 2 1 Liftoff