1Z0-829 Controlling Program Flow — Timed 40 Questions

Question 1

A developer writes code to iterate over a list of strings and print each element. The code uses an enhanced for loop. Which statement is true about the enhanced for loop?

Accepted Answer

It can be used with arrays and any object that implements Iterable.. The enhanced for loop (for-each) in Java can iterate over arrays and any object that implements the Iterable interface, which includes all Collection classes (e.g., List, Set, Queue). This is because the for-each loop internally uses an iterator for Iterable objects or array indexing for arrays, making it a versatile construct for traversing elements without needing an explicit counter.

Answer

It can only be used with arrays.

Answer

It requires an explicit counter variable.

Answer

It allows removing elements from the collection during iteration without ConcurrentModificationException.

Question 2

Given the code snippet:
int x = 10;
if (x > 5) {
    System.out.print("A");
} else if (x > 7) {
    System.out.print("B");
} else {
    System.out.print("C");
}
What is the output?

Accepted Answer

A. The if-else chain evaluates conditions sequentially. Since x=10 satisfies x > 5, the first block executes and prints 'A'. The else if and else branches are skipped entirely because the first condition was true. Thus, only 'A' is output.

Answer

C

Answer

ABC

Answer

B

Question 3

A method contains a try-with-resources statement that uses two resources: a FileInputStream and a BufferedInputStream. The FileInputStream constructor throws a FileNotFoundException. Which statement about resource closing is true?

Accepted Answer

No resources are closed because the FileInputStream constructor failed before any resource was opened.. In a try-with-resources statement, resources are closed only if they have been successfully initialized. If the FileInputStream constructor throws a FileNotFoundException, the resource is never created, so the try-with-resources statement does not attempt to close it. The BufferedInputStream is never constructed because the exception occurs before its declaration is reached, so no resources are opened and none need to be closed. Therefore, option C is correct.

Answer

The BufferedInputStream is closed if it was successfully created, but the FileInputStream is not.

Answer

Both resources are closed even if the FileInputStream constructor throws an exception.

Answer

The programmer must explicitly close the resources in a finally block.

Question 4

Which TWO statements are true about the switch statement in Java?

Accepted Answer

It can be used with String objects.. Java's switch statement supports String objects since Java 7, allowing comparison based on the string's hashCode() and equals() methods. Option D is correct because switch can be used as an expression (e.g., with the arrow syntax) that yields a value, which can be assigned to a variable or returned.

Answer

Case values can be variables that are not final.

Answer

It requires a default case.

Answer

Each case must have a unique code block.

Question 5

Which THREE statements are true about loops in Java?

Accepted Answer

The break statement can be used to exit a loop prematurely.. The break statement in Java is used to immediately terminate the execution of a loop (for, while, or do-while) and transfer control to the statement following the loop. This allows premature exit based on a condition, which is a fundamental control flow mechanism in Java.

Answer

A while loop always executes at least once.

Answer

A do-while loop may execute zero times if the condition is false.

Question 6

What is the output?

```java
int x = 10;
do {
    System.out.print(x);
} while (x-- > 10);
```

Accepted Answer

10. 10 because in the missing code, the loop condition likely uses pre-decrement or the print statement occurs before the decrement, so the first value printed is the initial value of x, which is 10. The post-decrement trap described in the current explanation does not apply.

Answer

9

Answer

15

Answer

6

Question 7

You are developing a high-frequency trading application that processes a stream of market data ticks. Each tick is represented by a Tick object with fields: long timestamp, String symbol, double price, int volume. Ticks arrive in real-time and must be processed in order. A bug is reported: the application occasionally processes a tick out of order, causing incorrect trade decisions. The processing logic uses a while loop to read from a blocking queue and process each tick. The code is: BlockingQueue queue = new LinkedBlockingQueue<>(); while (true) { Tick tick = queue.take(); process(tick); } After investigation, you find that the queue is fed by multiple producer threads that sometimes reorder ticks due to network delays. Which course of action best ensures ticks are processed in the correct chronological order without sacrificing throughput?

Accepted Answer

Replace LinkedBlockingQueue with a PriorityBlockingQueue that orders by timestamp.. PriorityBlockingQueue maintains elements in natural order (or by a provided Comparator), so ticks are automatically ordered by timestamp when inserted. This ensures the consumer always processes the chronologically earliest tick first, even if producers add them out of order, without requiring additional sorting or blocking.

Answer

Use a SynchronousQueue and have producers wait for the consumer to acknowledge.

Answer

After taking from the queue, sort a batch of ticks before processing.

Answer

Add a delay before processing to allow out-of-order ticks to arrive.

Question 8

Which loop construct guarantees that the body executes at least once?

Accepted Answer

do-while loop. The do-while loop is the only loop construct in Java that guarantees the body executes at least once because the condition is evaluated after the loop body. This post-test loop design ensures that regardless of the initial condition value, the body runs before any check occurs.

Answer

for loop

Answer

enhanced for loop

Answer

while loop

Question 9

Given the following Java code:

```java
for (int i = 0; i <= 2; i++) {
    for (int j = i; j <= i+2; j++) {
        if (j <= 3) {
            System.out.print(j + " ");
        }
    }
}
```

What is the output?

Accepted Answer

0 1 2 1 2 3 2 3. The program uses nested for loops. The outer loop iterates i from 0 to 2 (inclusive). For each i, the inner loop iterates j from i to i+2 (inclusive), but due to a condition that prevents printing values greater than 3, the inner loop effectively prints j only up to 3. Thus, for i=0 it prints 0,1,2; for i=1 it prints 1,2,3; for i=2 it prints 2,3. Combined on one line, the output is '0 1 2 1 2 3 2 3', which corresponds to option B.

Answer

0 1 2 1 2 3 2 3 4

Answer

0 1 2 1 2 3 2 3 4 5

Answer

0 1 2 1 2 3 2 3 3 4

Question 10

Which THREE statements about the switch statement in Java are correct?

Accepted Answer

The default case can be placed anywhere within the switch block.. The default case can be placed anywhere within the switch block according to the Java Language Specification. Option D is correct: case labels must be compile-time constant expressions; a final variable assigned a constant expression qualifies as a compile-time constant. Option E is correct: switch works with int, char, String, and enum types. Option B is incorrect because case values must be compile-time constants, not arbitrary runtime expressions. Option C is incorrect because break is not mandatory; it is optional and used to prevent fall-through.

Answer

Case values can be runtime expressions.

Answer

A break statement is mandatory after each case block.

Question 11

A Java application processes a list of orders. Each order has a status: NEW, PROCESSING, SHIPPED, or DELIVERED. The code must print a message based on the status:
- If NEW: "Order received"
- If PROCESSING: "Order in progress"
- If SHIPPED: "Order shipped"
- If DELIVERED: "Order delivered"
- For any other status: "Unknown status"

The developer writes the following code using a switch expression:

String message = switch (status) {
    case NEW -> "Order received";
    case PROCESSING -> "Order in progress";
    case SHIPPED -> "Order shipped";
    case DELIVERED -> "Order delivered";
    default -> "Unknown status";
};
System.out.println(message);

What is the correct course of action to ensure the code compiles and runs correctly?

Accepted Answer

No change needed; the code compiles and runs as expected.. The switch expression shown is syntactically valid and complete. It uses the arrow syntax with all enum constants covered and includes a default branch to handle any other status, so it compiles and runs as expected. Switch expressions can yield values and work with enum types, making the code correct as written.

Answer

Add a default branch to handle any other status.

Answer

Use if-else if statements because switch cannot be used with enum types.

Answer

Change the switch expression to a switch statement because switch expressions cannot yield values.

Question 12

Which TWO statements about the switch statement in Java are true?

Accepted Answer

A break statement is optional.. In a Java switch statement, the break statement is optional. If omitted, execution falls through to the next case (fall-through behavior), which can be intentional or lead to bugs. This is a core feature of the switch construct, not a requirement.

Answer

A switch statement can be used as an expression in all cases.

Answer

The switch expression can be of type long.

Answer

The case values can be variables.

Question 13

Given the following code fragment:
```java
int x = 0;
for (int i = 0; i < 4; i++) {
    x++;
}
System.out.println(x);
```
What is the result?

Accepted Answer

4. The loop runs four times (i = 0, 1, 2, 3), incrementing x each time. Therefore, x becomes 4, so the output is 4. Option B is correct.

Answer

9

Answer

3

Answer

5

Question 14

A Java developer is writing a batch processing application that reads records from a database and processes them. The processing must continue even if some records cause exceptions (e.g., data conversion errors). However, the application must log each failed record and its error, then continue with the next record. The developer uses a for loop to iterate over a list of records. Inside the loop, a try-catch block wraps the processing logic. After implementing, the developer notices that when an exception occurs, the loop terminates prematurely instead of continuing. The code structure is:

List<Record> records = fetchRecords();
for (Record rec : records) {
    try {
        process(rec);
    } catch (Exception e) {
        log.error("Failed to process: " + rec.getId(), e);
    }
}

What is the most likely reason for the premature termination?

Accepted Answer

The process() method throws an Error instead of an Exception.. The code catches `Exception`, but `Error` (and its subclasses like `OutOfMemoryError`, `StackOverflowError`, or custom `Error` types) are not subclasses of `Exception`. In Java, `Throwable` has two main branches: `Exception` (including `RuntimeException`) and `Error`. Since `Error` is not caught by `catch (Exception e)`, it propagates up and terminates the loop. This is the most likely reason for premature termination because the developer assumed all failures would be `Exception` types.

Answer

The records list contains null elements, causing a NullPointerException that is not caught.

Answer

The log.error() method itself throws an unchecked exception that is not caught.

Answer

The try-catch block is incorrectly placed inside the for loop, causing the loop to break on any exception.

Question 15

Order the steps to properly handle resources using try-with-resources in Java.

Accepted Answer

Step 1: Declare and initialize resources in the try-with-resources parentheses. Step 2: Use the resources in the try block. Step 3: Resources are automatically closed in reverse order of declaration.. try-with-resources ensures each resource is closed at the end of the statement. Resources are closed in the opposite order they were created.

Answer

Step 1: Use resources in try block. Step 2: Declare resources in try-with-resources. Step 3: Resources are closed in declaration order.

Answer

Step 1: Declare resources in try-with-resources. Step 2: Close resources manually in a finally block. Step 3: Use resources in try block.

Answer

Step 1: Use resources in try block. Step 2: Declare resources in try-with-resources. Step 3: Resources are closed automatically in declaration order.

Question 16

Order the steps to handle checked exceptions in a method that throws IOException.

Accepted Answer

1. Locate the code that throws IOException. 2. Enclose the code in a try block. 3. Add a catch block for IOException. 4. Provide exception handling code in the catch block.. Checked exceptions must be either caught or declared in the method signature. Unhandled checked exceptions cause compilation errors.

Answer

1. Locate the code that throws IOException. 2. Add a catch block for IOException. 3. Enclose the code in a try block. 4. Add a finally block.

Answer

1. Locate the code that throws IOException. 2. Add a finally block. 3. Add a try block. 4. Add a catch block.

Answer

1. Locate the code that throws IOException. 2. Continue writing code without any exception handling. 3. Assume the program will not throw IOException. 4. Compile and ignore errors.

Question 17

Match each Java module directive to its description.

Accepted Answer

requires: Specifies a dependency on another module.. Correct matches: requires specifies dependencies, exports grants compile-time access, opens enables reflective access, provides declares service implementations. Common confusion is between exports and opens due to their related but distinct roles.

Answer

exports: Allows reflective access to a package.

Answer

opens: Makes a package accessible to other modules.

Question 18

Match each I/O stream class to its description.

Accepted Answer

FileInputStream: Reads bytes from a file. The correct matches are based on the direction (read vs write) and type (byte vs character) of the stream. FileInputStream reads bytes; FileOutputStream writes bytes. BufferedReader reads characters with buffering; BufferedWriter writes characters with buffering.

Answer

FileInputStream: Writes bytes to a file

Answer

BufferedReader: Writes text to a character-output stream

Question 19

A developer writes a method that processes a grade and returns a message using a switch expression. The code is:

```java
public static String getMessage(int grade) {
    return switch (grade) {
        case 90, 80 -> "Excellent";
        case 70, 60 -> "Good";
        case 50 -> "Pass";
        default -> "Fail";
    };
}
```

Which statement is correct about this code?

Accepted Answer

The code compiles and runs correctly, returning the appropriate message.. The switch expression uses the arrow form with a list of constants per case, which is valid syntax in Java 14+. The arrow form does not require a 'yield' statement when the right side is a single expression or block; here, each case yields a string literal directly. The 'default' clause is mandatory in a switch expression to cover all possible values, and it is correctly included.

Answer

The code does not compile because the switch expression must be enclosed in parentheses.

Answer

The code does not compile because the arrow form requires a 'yield' statement.

Answer

The code does not compile because 'default' is not allowed in a switch expression.

Question 20

Given the following code snippet:

```java
outer:
for (int i = 0; i < 3; i++) {
    for (int j = 0; j < 3; j++) {
        if (i == 1 && j == 1) {
            break outer;
        }
        System.out.print(i + "-" + j + " ");
    }
}
```

What is the output?

Accepted Answer

0-0 0-1 0-2 1-0. The labeled `break outer;` statement exits the outer loop entirely when `i == 1` and `j == 1`. Before that condition is met, the inner loop prints pairs for `i=0` (all j values 0,1,2) and for `i=1` with `j=0`. When `i=1` and `j=1`, the break occurs, so `1-1` is never printed, and the outer loop stops, preventing any further iterations.

Answer

0-0 0-1 0-2 1-0 1-1 1-2

Answer

0-0 0-1 0-2 1-0 2-0 2-1 2-2

Answer

0-0 0-1 0-2 1-0 1-1