1Z0-811 Control Flow and Loops Practice Test 4 — 15 Questions

Question 1

A developer writes a loop that iterates over an array of integers. The loop should stop when it encounters a negative number. Which control flow construct best achieves this?

Accepted Answer

for loop with break inside if condition. A for loop with a break statement allows the developer to iterate over an array of integers and immediately exit the loop when a negative number is encountered. The break statement terminates the loop's execution unconditionally, making it the most direct and readable control flow construct for this requirement.

Answer

do-while loop

Answer

enhanced for loop with return

Answer

while loop with continue

Question 2

A company's application uses a switch statement to handle different user roles. The code currently has a bug where after processing one role, it unintentionally executes the next role's logic. Which concept is being misused?

Accepted Answer

Missing break statements causing fall-through. In Java, a switch statement without break statements causes fall-through, where execution continues into subsequent case blocks even after a match is found. This is exactly the bug described: after processing one role, the code unintentionally executes the next role's logic because no break terminates the case.

Answer

Incorrect default case

Answer

Using enum in switch

Answer

Using string in switch (Java 7+)

Question 3

A developer implements a loop that processes a list of transactions. The loop must ensure that at least one transaction is processed even if the list is empty. Which loop construct guarantees this?

Accepted Answer

do-while loop. The do-while loop is the correct choice because it guarantees that the loop body executes at least once, regardless of the condition. In Java, the do-while loop evaluates its boolean condition after executing the loop body, so even if the list is empty (e.g., size 0), the transaction processing code inside the loop will run once before the condition is checked.

Answer

while loop

Answer

enhanced for loop

Answer

for loop

Question 4

In a Java method, a developer needs to skip the current iteration and move to the next when a certain condition is met inside a for loop. Which statement should be used?

Accepted Answer

continue;. The `continue` statement in Java immediately skips the remaining code in the current iteration of a loop and proceeds to the next iteration. This is exactly what the developer needs when a condition is met inside a `for` loop to move to the next cycle without executing further statements in the current iteration.

Answer

return;

Answer

exit;

Answer

break;

Question 5

A junior developer wrote a while loop that never terminates. What is the most likely cause?

Accepted Answer

The loop condition is always true. A while loop terminates only when its boolean condition evaluates to false. If the condition is always true, the loop will run indefinitely, causing an infinite loop. In Java, this typically happens when the loop variable is not updated or the condition logic is flawed.

Answer

The loop variable is incremented correctly

Answer

The loop uses a for structure

Answer

The loop body contains a break statement

Question 6

A developer needs to iterate over a 2D array row by row and exit early if a specific value is found in any cell. Which nested loop structure with control statements is most efficient?

Accepted Answer

Outer for with inner for, use labeled break. A labeled break allows the developer to exit both the inner and outer loops immediately when the target value is found. This is the most efficient approach for a row-by-row search in a 2D array, as it avoids unnecessary iterations after the value is located. Using a labeled break provides precise control over nested loop termination without requiring additional flags or method extraction.

Answer

Outer for with inner for, use return

Answer

Outer while with inner for, use continue

Answer

Outer do-while with inner while, use break without label

Question 7

Which two statements about the break statement in Java are true?

Accepted Answer

break can be used inside a switch case. The break statement is used inside a switch case to terminate the switch block and prevent fall-through to subsequent cases. Without break, execution would continue into the next case, which is often unintended.

Answer

break can be used without any enclosing loop

Answer

break is used to skip to next iteration

Answer

break exits the current loop iteration

Question 8

Given the code fragment:

```java
int[] data = {1, 2, 3, 4, 5};
int sum = 0;
for (int i = 0; i <= data.length; i++) {
    sum += data[i];
}
System.out.println(sum);
```

What is the result?

Accepted Answer

ArrayIndexOutOfBoundsException. The loop condition i <= data.length causes i to become 5 when data.length is 5, but valid indices are 0-4. This results in an ArrayIndexOutOfBoundsException. Option A is wrong because the exception occurs before sum reaches 15. Option C is wrong because sum is not 0. Option D is wrong because the code compiles successfully.

Answer

15

Answer

0

Answer

Compilation fails

Question 9

A developer receives a ticket that a batch processing job is running indefinitely. The job reads records from a database and processes them in a loop. The code uses a while(true) loop with a break condition when a sentinel value is encountered. However, due to a data anomaly, the sentinel value is never reached, causing the loop to run forever. The developer needs to fix the loop to prevent infinite execution while still allowing processing of all records until the sentinel is reached. Which approach is most appropriate?

Accepted Answer

Add a counter variable and break after a maximum number of iterations. Adding a counter variable and breaking after a maximum number of iterations provides a safety net against infinite loops while still allowing the loop to process all records until the sentinel is reached under normal conditions. This approach is a common defensive programming technique in Java to handle unexpected data anomalies without altering the core loop logic.

Answer

Use a do-while loop that checks the condition at the end

Answer

Change the loop to a for loop with a fixed range based on the expected number of records

Answer

Throw an exception when the loop runs too long

Question 10

A developer is writing a method to find the first occurrence of a negative number in an array and return its index, or -1 if none found. The current implementation uses a for loop with an if condition and a return when found. However, the method throws a NullPointerException when the array is null. The developer wants to handle this edge case gracefully and still return -1. Which approach is most appropriate?

Accepted Answer

Add a null check at the beginning of the method and return -1 if null. It directly checks if the array reference is null before any iteration, returning -1 immediately. This is the simplest and most efficient way to handle a null input, avoiding any attempt to access the array's length or elements, which would throw a NullPointerException. The method's contract is preserved by returning -1 when no negative number is found, including the case of a null array.

Answer

Use an enhanced for loop with a null check

Answer

Use a try-catch block inside the loop

Answer

Use a while loop with a null check inside

Question 11

A developer writes the following method to search a sorted int array for a target value:

```java
public static int search(int[] arr, int target) {
    int lo = 0, hi = arr.length - 1;
    while (lo <= hi) {
        int mid = (lo + hi) / 2;
        if (arr[mid] == target) {
            return mid;
        } else if (arr[mid] < target) {
            lo = mid;
        } else {
            hi = mid;
        }
    }
    return -1;
}
```

When the method is called with a target that exists in the array, the method sometimes never returns. Which change fixes the defect?

Accepted Answer

Change `lo = mid;` to `lo = mid + 1;` and `hi = mid;` to `hi = mid - 1;`. Binary search requires that each iteration strictly reduces the candidate range. Assigning lo or hi to mid without a plus or minus one leaves mid inside the window, so when the window has two elements the same pair can be examined repeatedly and the loop never exits. Moving the bounds one step past mid excludes the already-tested element and guarantees termination.

Answer

Change the loop condition from `lo <= hi` to `lo < hi`

Answer

Change the return type from int to boolean and return false instead of -1

Answer

Change `int mid = (lo + hi) / 2;` to `int mid = (lo + hi + 1) / 2;`

Question 12

A developer is writing a utility that must print each character of a String on its own line. The code is:

```java
String word = "Java";
for (int i = 0; i <= word.length(); i++) {
    System.out.println(word.charAt(i));
}
```

When run, the program prints the four characters correctly but then throws an exception. What is the cause and the correct fix?

Accepted Answer

The condition should be `i < word.length()`, because valid indices run from 0 to length() - 1 and index length() is out of range. The loop condition i <= word.length() allows one iteration too many. Because charAt accepts indices from 0 through length() - 1, the final pass attempts to read a nonexistent position and throws StringIndexOutOfBoundsException. Replacing the inclusive comparison with a strict less-than comparison keeps every access inside the valid range.

Answer

The condition should be `i <= word.length() - 1` and the loop variable must be declared outside the for statement

Answer

The call to println should be changed to print, because println cannot accept a char argument

Answer

The loop variable should start at 1 instead of 0, because charAt is one-based

Question 13

A developer is writing a method that prints the numbers 1 through 5. The method must stop printing as soon as the number 3 has been printed, without printing any further numbers. Which loop control statement should be used inside the loop body when the current value equals 3?

Accepted Answer

break;. The break statement exits the innermost loop immediately, which is exactly what is needed to stop printing after the value 3. The continue statement only skips the current iteration and would keep printing later values, while return and System.exit are too broad, ending the method or the whole JVM rather than just the loop.

Answer

return;

Answer

continue;

Answer

System.exit(0);

Question 14

A developer is writing a Java method that must return the smallest even number in an int array. If no even number exists, the method must return -1. The developer writes:

public static int firstEven(int[] nums) {
    for (int i = 0; i < nums.length; i++) {
        if (nums[i] % 2 == 0) {
            return nums[i];
        }
    }
    return -1;
}

Which statement describes the behavior of this method?

Accepted Answer

The method returns the first even number encountered in the array, not necessarily the smallest even number.. The loop exits as soon as an even value is found, so the method returns the first even element in index order. That value is only the smallest if the array happens to be sorted ascending. Finding a minimum requires explicit comparison against a running candidate, or sorting the array before the search.

Answer

The method returns -1 whenever the array is not sorted in ascending order.

Answer

The method returns the smallest even number because the loop visits elements in ascending index order.

Answer

The method always returns -1 because the return statement inside the loop is unreachable.

Question 15

A developer needs to iterate over an array of department names and print each one. The array may contain null entries, and the code must handle a null entry by printing the text "unknown" instead of causing a NullPointerException. Which loop construct is most appropriate for iterating over the array while still allowing a null check before each element is used?

Accepted Answer

A traditional for loop with an index, checking each element for null before use.. A traditional for loop with an index lets the code examine each array slot directly, so a null check can be applied before printing. The enhanced for loop would still throw a NullPointerException if a method is called on a null element without a guard, and the other loop forms introduce incorrect execution order or assumptions about array contents.

Answer

A do-while loop that assumes the array is non-empty and accesses elements without bounds checking.

Answer

A while loop that increments the index before checking the array length.

Answer

An enhanced for loop (for-each) that directly calls a method on each element without checking for null.