1Z0-829 Practice Test 16 — 15 Questions

Question 1

A developer creates a custom runtime image with jlink for a Java 17 application. The command is: jlink --module-path $JAVA_HOME/jmods:mods --add-modules com.acme.app --output image. The application calls java.util.logging.Logger and java.sql.DriverManager at runtime. After launching image/bin/java, the application throws NoClassDefFoundError for java.sql.DriverManager. Which action resolves the failure?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Add --add-modules java.sql to the jlink command so the java.sql module is included in the image.. jlink builds an image from a set of root modules and their transitive requires. If application code depends on java.sql without a corresponding requires directive, that module is excluded and its classes are unavailable at runtime. Adding java.sql as an explicit root with --add-modules includes the module and its classes, resolving the NoClassDefFoundError. Options controlling services, debug info, or compression do not affect module inclusion.

Answer

Add --bind-services to the jlink command so service provider modules are resolved automatically.

Answer

Add --compress=2 to the jlink command so compressed classes are decompressed on demand, including java.sql.

Answer

Add --strip-debug to the jlink command to reduce image size and prevent class loading conflicts.

Question 2

A Java application uses a custom ObjectInputStream to deserialize configuration objects from a trusted internal network. A security audit recommends adding a serialization filter to restrict classes. The application already overrides resolveClass to allow only classes in a specific package. Which statement about combining these mechanisms is true?

Accepted Answer

The serialization filter is applied before resolveClass, so it can reject classes even if resolveClass would allow them.. The serialization filter is evaluated before class resolution, so it can block classes even if a custom resolveClass would allow them. This provides an additional layer of security. The two mechanisms do not conflict; they work together. The filter is not limited to non-Serializable classes; it applies to all classes in the stream. Combining them is safe and recommended for defense in depth.

Answer

The custom resolveClass override takes precedence and the filter is ignored.

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Combining both mechanisms causes a conflict and leads to a SecurityException at runtime.

Answer

The filter can only reject classes that are not Serializable, so it has no effect on Serializable classes.

Question 3

A financial application processes a Stream of transaction amounts. A developer writes: Optional total = amounts.reduce((a, b) -> a + b); If the stream is empty, what happens when the developer calls total.orElseThrow()?

Accepted Answer

A NoSuchElementException is thrown.. The single-argument reduce returns an Optional because an empty stream has no result and no identity to fall back on. For an empty stream the Optional is empty, and orElseThrow() translates that emptiness into a NoSuchElementException. To avoid this, supply an identity with the two-argument reduce or handle the empty case explicitly.

Answer

An IllegalStateException is thrown.

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null is returned.

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The value 0 is returned.

Question 4

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.

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

Answer

It provides an implicit counter variable that can be accessed.

Question 5

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 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

A developer needs to copy a large directory tree from one location to another, preserving file attributes. Which method should be used?

Accepted Answer

Implement a FileVisitor using Files.walkFileTree and copy each file with COPY_ATTRIBUTES. `Files.walkFileTree` with a custom `FileVisitor` allows you to recursively traverse a directory tree and copy each file individually using `Files.copy` with `StandardCopyOption.COPY_ATTRIBUTES`. This is necessary because `Files.copy` on a directory does not copy the directory tree recursively; it only copies the top-level directory entry. The `FileVisitor` pattern ensures that subdirectories and files are visited and copied in depth-first order, preserving file attributes at each step.

Answer

Files.copy(source, target, StandardCopyOption.COPY_ATTRIBUTES)

Answer

Use Files.walk() and then Files.copy() for each entry

Answer

Use FileUtils.copyDirectory from Apache Commons IO

Question 8

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

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BufferedReader: Writes text to a character-output stream

Question 9

Given: for(int i=0; i<3; i++) { for(int j=0; j<3; j++) { if(i==1 && j==1) break; } } What is the value of i after the outer loop completes?

Accepted Answer

3. The outer loop variable `i` increments from 0 to 2. When `i` is 1 and `j` is 1, the `break` statement exits only the inner `for` loop, not the outer loop. The outer loop continues to its next iteration, incrementing `i` to 2, then to 3. When `i` becomes 3, the outer loop condition `i < 3` fails, so the loop terminates. Thus, after the outer loop completes, `i` is 3.

Answer

1

Answer

2

Answer

4

Question 10

A developer runs 'java --list-modules' and sees the output above. Which command can be used to create a custom runtime image containing only the 'java.base' module?

Accepted Answer

jlink --add-modules java.base --output myimage. The `jlink` tool is used to assemble and optimize a set of modules and their dependencies into a custom runtime image. The `--add-modules` option specifies which modules to include, and `--output` specifies the target directory. Option D correctly uses `jlink --add-modules java.base --output myimage` to create a runtime image containing only the `java.base` module.

Answer

jar --create --file myimage --module java.base

Answer

jimage --add-modules java.base --output myimage

Answer

jlink --modules java.base --output myimage

Question 11

Which THREE statements are true about HashSet in Java 17? (Choose three.)

Accepted Answer

Does not maintain insertion order. Option A is correct because HashSet is backed by a HashMap and does not preserve insertion order; iteration order is unspecified and can change as elements are added or removed. Option D is correct because HashSet offers constant-time (O(1)) average performance for basic operations such as add, remove, and contains, assuming a well-distributed hash function. Option E is correct because HashSet permits at most one null element, since it stores elements as keys in the underlying HashMap and duplicate keys are not allowed. Option B is incorrect because HashSet does not allow duplicate elements; adding an existing element leaves the set unchanged. Option C is incorrect because HashSet is not thread-safe; concurrent modification requires external synchronization or a wrapper such as Collections.synchronizedSet.

Answer

Allows duplicate elements

Answer

Is thread-safe

Question 12

Which statement about the Stream API is true?

Accepted Answer

A stream can be consumed only once.. A Stream in Java represents a sequence of elements that can be traversed only once. Once a terminal operation (like collect() or forEach()) is invoked on a stream, the stream is consumed and cannot be reused; attempting to do so throws an IllegalStateException. This one-time consumption is a fundamental design principle of the Stream API, ensuring that operations are applied to a single, immutable pipeline.

Answer

Parallel streams always improve performance.

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Streams are always finite.

Answer

Intermediate operations are executed eagerly.

Question 13

Which of the following is a best practice when designing custom exception classes?

Accepted Answer

Extend an existing exception class and provide constructors that call the superclass constructor.. The Java best practice for custom exceptions is to extend an existing exception class (e.g., Exception or RuntimeException) and provide constructors that call the superclass constructor. This ensures the custom exception inherits the standard exception mechanism, including proper chaining, stack trace handling, and compatibility with try-catch blocks, without reinventing the wheel.

Answer

Define a custom exception with a single constructor that takes an int error code.

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Extend the Throwable class directly to create a new exception type.

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Use a generic Exception class with a string message to indicate the type of error.

Question 14

Which TWO statements are true about creating an unmodifiable List?

Accepted Answer

Collections.unmodifiableList() returns a view that is unmodifiable, but the backing list can still be changed.. Option A is correct because Collections.unmodifiableList() returns a read-only view backed by the original list; attempts to modify the view throw UnsupportedOperationException, but changes made directly to the backing list remain visible through the view. Option B is correct because List.of() returns a truly immutable list whose mutator methods (add, set, remove, etc.) throw UnsupportedOperationException, and it also rejects null elements. Option C is wrong because List.copyOf() creates an unmodifiable snapshot copy, so later changes to the source list do not affect the copy. Option D is wrong because new ArrayList<>(Arrays.asList(...)) produces a normal, fully modifiable ArrayList. Option E is wrong because Arrays.asList() returns a fixed-size list backed by the array: set() works, but add() and remove() throw UnsupportedOperationException, so it is not unmodifiable.

Answer

List.copyOf() creates a list that, if the source list is changed, the copy also changes.

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new ArrayList<>(Arrays.asList(...)) creates an unmodifiable list.

Answer

Arrays.asList() returns an unmodifiable list.

Question 15

Which TWO are true about the PriorityQueue class?

Accepted Answer

It is not thread-safe.. Option C is correct because PriorityQueue is an unsynchronized collection; it does not internally guard its state, so concurrent access from multiple threads requires external synchronization (e.g., wrapping with Collections.synchronizedQueue or using PriorityBlockingQueue). Option D is correct because PriorityQueue offers a constructor PriorityQueue(int initialCapacity, Comparator comparator) and PriorityQueue(Comparator comparator), allowing a custom Comparator to define the ordering instead of natural ordering. Option A is wrong because PriorityQueue does not permit null elements; adding null throws NullPointerException (nulls are also disallowed because ordering would be undefined). Option B is wrong because PriorityQueue orders elements by their natural ordering or by the supplied Comparator, not by insertion order. Option E is wrong because contains() performs a linear scan, giving O(n) time, not O(1).

Answer

It allows null elements.

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It orders elements based on insertion order.

Answer

It provides O(1) time for contains().