1Z0-811 Control Flow and Loops — 30 Questions

Question 1

A developer writes a loop to iterate over an array of integers. The loop must sum all elements and stop early if the sum exceeds 100. Which control flow construct should be used?

Accepted Answer

for(int i=0; i<arr.length; i++) { sum += arr[i]; if(sum > 100) break; }. Both Option B and Option D are correct. Option B uses a standard for loop with an index, allowing direct array access and an early break when sum exceeds 100. Option D uses an enhanced for-each loop, which also correctly iterates over all elements and exits via break when the condition is met. Option A is incorrect because the while(true) loop has no termination condition and lacks array bounds checking. Option C is incorrect because the do-while loop checks the condition after the body, causing one extra iteration if the sum exceeds 100 during the loop.

Answer

while(true) { sum += arr[i]; i++; }

Answer

do { sum += arr[i]; i++; } while(i<arr.length && sum <= 100);

Question 2

Which statement about the for-each loop in Java is true?

Accepted Answer

It cannot be used with arrays.. The for-each loop (enhanced for loop) in Java can be used with arrays and collections. However, if you attempt to remove elements from a collection while iterating using a for-each loop without using an Iterator's remove() method or other concurrent modification handling, a ConcurrentModificationException will be thrown. Therefore, additional logic is required to safely remove elements during iteration. Option D is false because the for-each loop can indeed be used with arrays; it iterates over each element in the array. Options B and C are also false as the for-each loop cannot modify array elements (assigning to the loop variable does not affect the array) and it always iterates in forward order only.

Answer

It cannot remove elements from a collection during iteration without additional logic.

Answer

It can modify the array elements.

Answer

It can iterate in reverse order.

Question 3

A developer implements a menu-driven application using a switch statement inside a do-while loop. The menu options are 1-4, and option 4 is supposed to exit the application. However, after selecting option 4, the menu is displayed again before the application exits. The code is structured as follows:
do {
    displayMenu();
    choice = scanner.nextInt();
    switch(choice) {
        case 1: // process option 1
        break;
        case 2: // process option 2
        break;
        case 3: // process option 3
        break;
        case 4: break; // intended to exit loop
    }
} while(choice != 4);
The developer realizes that the break inside the switch only exits the switch, not the loop. What is the correct fix?

Accepted Answer

Use a labeled break to exit the loop. Use a labeled break to exit the loop. The issue is that the break statement inside the switch only exits the switch block, not the do-while loop. A labeled break allows the program to break out of the outer loop directly. For example:
outerLoop:
do {
    displayMenu();
    choice = scanner.nextInt();
    switch(choice) {
        case 1: ...
        case 4: break outerLoop;
    }
} while(choice != 4);

Option B is incorrect because continue would skip the rest of the current iteration and re-evaluate the loop condition, but it does not exit the loop. Option C is incorrect because replacing with an if-else chain does not inherently provide a way to exit the loop; you would still need to set a flag or use a labeled break. Option D is incorrect because although setting a flag could work, it is not necessary; a labeled break is a more direct and clean solution in Java.

Answer

Use a continue statement instead of break

Answer

Replace the switch with an if-else chain

Answer

Set a flag variable to true and check it in the loop condition

Question 4

Which loop is guaranteed to execute its body at least once?

Accepted Answer

do-while loop. The do-while loop is a post-test loop, meaning the condition is evaluated after the loop body executes. This guarantees that the body runs at least once, regardless of whether the condition is initially true or false. In Java, the do-while loop syntax is `do { ... } while (condition);`.

Answer

repeat-until loop

Answer

while loop

Answer

for loop

Question 5

A developer needs to implement a menu-driven program that repeatedly displays options, reads input, and processes the choice until the user selects 'Exit'. Which loop structure and control flow is most appropriate?

Accepted Answer

do-while loop with switch statement. A do-while loop guarantees at least one iteration, which is ideal for menu-driven programs where the menu must be displayed before any input is processed. The switch statement provides a clean, readable way to handle multiple discrete choices (like menu options) compared to a chain of if-else statements, and it aligns with Java's control flow best practices for such scenarios.

Answer

for loop with break condition and nested if-else

Answer

for(;;) loop with if-else chain

Answer

while(true) loop with if-else chain

Question 6

What is the output of the following code?

int i = 0;
while (i < 5) {
    if (i == 3) {
        i++;
        continue;
    }
    System.out.print(i + " ");
    i++;
}

Accepted Answer

0 1 2 4. The while loop iterates while i < 5. When i equals 3, the if condition triggers, incrementing i to 4 and then using continue to skip the print statement for that iteration. Thus, 3 is never printed, and the loop prints 0, 1, 2, and then 4 before i becomes 5 and the loop ends.

Answer

0 1 2 3

Answer

0 1 2 4 5

Answer

0 1 2 3 4

Question 7

A developer writes: for(int i=0; i<10; i++) { if(i%2==0) continue; System.out.print(i); }. What is the output?

Accepted Answer

13579. The loop iterates from i=0 to i=9. The `continue` statement skips the rest of the loop body when the condition `i%2==0` is true (i.e., when i is even). Therefore, only odd values of i (1, 3, 5, 7, 9) are printed, producing the output '13579'. Option B is correct.

Answer

0123456789

Answer

02468

Answer

123456789

Question 8

Which loop best suits a scenario where the number of iterations is unknown and depends on user input?

Accepted Answer

while loop. The while loop is best when the number of iterations is unknown and depends on user input because it evaluates a boolean condition before each iteration, allowing the loop to continue as long as the condition remains true. This is ideal for scenarios like reading user input until a sentinel value is entered, where the exact number of iterations cannot be predetermined.

Answer

for loop

Answer

for-each loop

Answer

do-while loop

Question 9

Which THREE statements are true about the switch statement in Java? (Choose three.)

Accepted Answer

Without a break statement, execution falls through to the next case.. Options C, D, and E are true. Option C correctly describes fall-through behavior: without a break statement, execution continues to the next case. Option D correctly states that the default case is optional. Option E is true because, since Java 7, the switch statement can be used with String objects. Options A and B are false: A is incorrect because switch does not support boolean expressions; B is incorrect because the default case can appear anywhere in the switch block.

Answer

It can be used with boolean expressions.

Answer

The default case must be placed at the end of the switch block.

Question 10

Which THREE statements are true about the break and continue statements in Java? (Choose three.)

Accepted Answer

A labeled break can be used to exit an outer loop.. A labeled break in Java allows you to specify a label on an outer loop and then use 'break label;' to exit that outer loop directly, not just the innermost loop. This is useful for breaking out of nested loops when a condition is met in an inner loop.

Answer

The continue statement can be used to exit a loop entirely.

Answer

The break statement cannot be used outside a loop.

Question 11

What is the output of the code?

```java
for (int i = 0; i < 5; i++) {
    if (i == 2) {
        continue;
    }
    System.out.print(i + " ");
}
```

Accepted Answer

0 1 3 4. The code uses a for loop that iterates from i = 0 to i < 5 (i.e., 0 through 4). Inside the loop, there is an if condition that checks if i equals 2. When i == 2, the continue statement is executed, which skips the rest of that iteration, so the System.out.print statement is not executed for i = 2. Therefore, the loop prints 0, 1, 3, and 4, each followed by a space. Option D correctly lists this output.

Answer

0 1 2 3 4

Answer

1 3 4

Answer

0 1 2 3

Question 12

What is the value of sum printed?

int sum = 0;
for (int i = 0; i < 3; i++) {
    sum = sum + i;
}
System.out.println(sum);

Accepted Answer

3. The loop initializes sum to 0 and iterates i from 0 to 2 inclusive. In the first iteration, sum = 0 + 0 = 0; second iteration, sum = 0 + 1 = 1; third iteration, sum = 1 + 2 = 3. After the loop, sum is printed, so the output is 3. Option C is correct.

Answer

6

Answer

0

Answer

1

Question 13

You are tuning a real-time data processing application that reads sensor data from a queue. The system must process each sensor reading, but occasionally a reading is invalid (null) and should be skipped. The loop must run indefinitely until the application is shut down gracefully. The current implementation uses a while(true) loop with a break condition when a shutdown flag is set. However, the loop is consuming excessive CPU because it continuously polls the queue even when no data is available. You need to modify the loop to reduce CPU usage while still processing data efficiently. Which approach should you take?

Accepted Answer

Replace the polling mechanism with a blocking queue that blocks until data is available.. Using a blocking queue (e.g., `BlockingQueue.take()`) causes the consumer thread to block automatically until data becomes available, eliminating busy-waiting and drastically reducing CPU usage. This is the standard pattern for producer-consumer scenarios in Java, as it leverages the underlying `notify`/`wait` mechanism to avoid polling overhead.

Answer

Change the while(true) loop to a for loop that iterates a fixed number of times.

Answer

Add a Thread.sleep(100) inside the loop to reduce polling frequency.

Answer

Use a do-while loop with a Thread.yield() call to give other threads CPU time.

Question 14

Arrange the steps to define a class with a main method in Java in the correct order.

Accepted Answer

Step 1: Declare the class, Step 2: Define the main method, Step 3: Add other members, Step 4: Write code in main, Step 5: Compile and run. First declare the class, then define the main method, add other members, write code in main, and finally compile and run.

Answer

Step 1: Declare the class, Step 2: Add other members, Step 3: Define the main method, Step 4: Write code in main, Step 5: Compile and run

Answer

Step 1: Define the main method, Step 2: Declare the class, Step 3: Add other members, Step 4: Write code in main, Step 5: Compile and run

Answer

Step 1: Declare the class, Step 2: Write code in main, Step 3: Define the main method, Step 4: Add other members, Step 5: Compile and run

Question 15

Match each Java operator to its description.

Accepted Answer

==: Compares two values for equality. The correct matches are: == for equality, && for logical AND. Common confusions include mixing assignment (=) with comparison (==) and misunderstanding the ternary operator vs. logical operators.

Answer

!=: Used to assign a value to a variable

Answer

instanceof: Used to compare two primitive values

Answer

?:: Used to perform a logical OR operation

Question 16

A developer needs to iterate over an array of integers and compute the sum of its elements. Which loop construct is most appropriate for this task?

Accepted Answer

Enhanced for loop. The enhanced for loop (for-each) is the most appropriate construct for iterating over an array of integers to compute a sum because it provides a concise, read-only traversal without needing an explicit index or iterator. It directly accesses each element in sequence, reducing boilerplate and the risk of off-by-one errors, which is ideal for aggregation operations like summation.

Answer

while loop

Answer

switch statement

Answer

do-while loop

Question 17

A programmer writes a switch statement to handle different cases. The code compiles and runs, but the output is unexpected: 'A' prints when the input is 'B'. Which is the most likely cause?

Accepted Answer

A break statement is missing after the case 'B'.. In a switch statement, when a case matches, execution continues sequentially through subsequent cases (fall-through) unless a break statement is encountered. If case 'B' lacks a break, after executing its code, the program falls through to the code for case 'A' (or the next case), printing 'A' even though the input was 'B'. This is the classic fall-through behavior in Java.

Answer

The switch variable type is char but should be String.

Answer

The switch statement is missing a default case.

Answer

The default case is executed instead of the matched case.

Question 18

In a nested loop structure, a developer wants to exit completely from the outer loop when a certain condition is met inside the inner loop. Which approach is correct?

Accepted Answer

Use a labeled break statement (e.g., break outerLabel;).. Java's labeled break statement allows a developer to specify an outer loop label and break out of that loop entirely from within an inner loop. This is the only control flow mechanism designed to exit multiple nested loops at once, as a plain break only exits the innermost loop.

Answer

Use a return statement within the inner loop.

Answer

Use a continue statement with a label.

Answer

Use a break statement inside the inner loop.

Question 19

Which THREE of the following are valid loop constructs in Java?

Accepted Answer

while loop. The correct answers are A (while loop), B (for loop), and E (do-while loop) because all three are valid loop constructs in Java. The while loop repeats as long as a condition is true, the for loop provides a compact iteration mechanism, and the do-while loop guarantees at least one execution.

Answer

switch statement

Answer

if statement

Question 20

Which THREE of the following are valid types that can be used as a switch expression in Java (as of Java 8)?

Accepted Answer

String. In Java 8, a switch expression can use `String`, `char`, and `int` as valid types. `String` was added in Java 7, and `char` and `int` are among the original primitive types supported. `long` and `boolean` are not allowed because `long` is a 64-bit type not supported by the switch statement's underlying `tableswitch` or `lookupswitch` bytecode instructions, and `boolean` has only two values, making it unsuitable for switch's multi-branch logic.

Answer

long

Answer

boolean