1Z0-829 Timed Practice Test 5 — 10 Questions

Question 1

Which THREE statements about lambda expressions are true? (Choose three.)
A. A lambda expression can be assigned to a functional interface variable.
B. A lambda expression can access final or effectively final local variables.
C. A lambda expression can throw any checked exception.
D. A lambda expression can be used to create an instance of an abstract class.
E. A lambda expression can be used to implement multiple abstract methods.

Accepted Answer

A lambda expression can throw any checked exception.. Option A is correct because a lambda expression can be assigned to a variable of a functional interface type. The lambda provides the implementation for the single abstract method of that interface, and the assignment is valid as long as the lambda's parameter types and return type match the method signature.

Answer

A lambda expression can be used to implement multiple abstract methods.

Answer

A lambda expression can be used to create an instance of an abstract class.

Question 2

A developer writes the following code using the Stream API:

List<String> list = List.of("a", "b", "c");
String result = list.stream().reduce("", (s1, s2) -> s1 + s2);
System.out.println(result);

What is the output?

Accepted Answer

abc. The correct answer is A because the `reduce` method with an identity value (`""`) and a binary operator (`(s1, s2) -> s1 + s2`) accumulates the stream elements in encounter order. Starting from the identity, it concatenates each element: `"" + "a" = "a"`, then `"a" + "b" = "ab"`, then `"ab" + "c" = "abc"`. The result is a `String`, not an `Optional`, because an identity is provided.

Answer

a

Answer

Optional[abc]

Answer

cba

Question 3

What does the following code print?

List<Integer> list = List.of(1, 2, 3, 4, 5);
list.stream().filter(i -> i % 2 == 0).forEach(System.out::print);

Accepted Answer

24. The correct answer is D because the stream filters only even numbers (i % 2 == 0) from the list, producing 2 and 4, which are then printed sequentially via forEach. The filter operation retains elements where the predicate is true, so only 2 and 4 satisfy the condition.

Answer

No output

Answer

12345

Answer

135

Question 4

Which TWO are valid lambda expressions? (Choose two.)
A. (int a, int b) -> a + b
B. a, b -> a + b
C. (a, b) -> a + b
D. (a, b) -> { a + b; }
E. (int a, b) -> a + b

Accepted Answer

(a, b) -> a + b. Option B is correct because a lambda expression with inferred parameter types can omit the parameter types and parentheses when there is exactly one parameter, but here there are two parameters, so parentheses are required. Option C is correct because it explicitly declares the types of both parameters, which is valid syntax for a lambda expression that returns the sum of the two integers.

Answer

a, b -> a + b

Answer

(a, b) -> { a + b; }

Answer

(int a, b) -> a + b

Question 5

Which TWO statements about the Stream API are correct? (Choose two.)
A. A stream can be traversed multiple times.
B. The peek() method is an intermediate operation.
C. The findFirst() method returns an Optional.
D. The collect() method is an intermediate operation.
E. The map() method returns a stream of the same type.

Accepted Answer

The peek() method is an intermediate operation.. Option A is correct because the `peek()` method is an intermediate operation in the Stream API. Intermediate operations return a new stream and are lazy; they are not executed until a terminal operation is invoked. `peek()` allows you to inspect elements as they flow through the pipeline without modifying them.

Answer

The collect() method is an intermediate operation.

Answer

A stream can be traversed multiple times.

Answer

The map() method returns a stream of the same type.

Question 6

A company uses CI/CD to build and package a Java 17 application. They want to produce a single executable JAR that includes all dependencies. Which tool should be used to achieve this?

Accepted Answer

Maven Shade Plugin. The Maven Shade Plugin (B) is the correct choice because it creates an uber-JAR (fat JAR) by merging all project dependencies into a single executable JAR, including transitive dependencies. It also provides a relocation feature to avoid classpath conflicts, which is essential for producing a self-contained artifact for deployment.

Answer

Maven JAR Plugin

Answer

Java jar command

Answer

jlink tool

Question 7

A developer has a module named 'com.example.app' that exports a package 'com.example.api'. Another module 'com.example.client' requires 'com.example.app'. Which directive must be in the module-info.java of 'com.example.client'?

Accepted Answer

requires com.example.app;. Option D is correct because the 'requires' directive in a module-info.java file declares a dependency on another module. For 'com.example.client' to access the exported packages of 'com.example.app', it must include 'requires com.example.app;'. This is the standard mechanism for module dependency in the Java Platform Module System (JPMS).

Answer

opens com.example.app;

Answer

uses com.example.api;

Answer

exports com.example.api;

Question 8

A developer is designing a service that processes multiple files concurrently. To avoid resource leaks, which practice is essential?

Accepted Answer

Use try-with-resources for each AutoCloseable resource. Option B is correct because try-with-resources guarantees that each AutoCloseable resource is closed automatically at the end of the statement, even if an exception occurs. This is essential when processing multiple files concurrently, as it prevents resource leaks without requiring explicit close() calls in finally blocks.

Answer

Ensure each thread has its own copy of the file handle

Answer

Call close() on each stream in a separate try-catch block

Answer

Use FileLock to prevent concurrent access

Question 9

Which statement about java.io and java.nio.file packages is true?

Accepted Answer

The java.nio.file package provides support for symbolic links and file attributes. Option A is correct because the java.nio.file package (part of NIO.2) explicitly provides support for symbolic links via methods like Files.createSymbolicLink() and Files.isSymbolicLink(), and it offers comprehensive file attribute access through classes like BasicFileAttributes, DosFileAttributes, and PosixFileAttributes, which are not available in java.io.

Answer

Classes in java.nio.file are thread-safe by default

Answer

The java.io package includes the Path interface

Answer

The java.nio.file package is deprecated in favor of java.io

Question 10

An application must read a configuration file that is updated frequently by another process. The developer wants to avoid stale data and minimize I/O operations. Which approach is best?

Accepted Answer

Use java.nio.file.WatchService to monitor the file for modifications and reload when notified. Option A is correct because java.nio.file.WatchService provides an event-driven mechanism to monitor file system changes, such as modifications to a configuration file. This approach avoids stale data by reloading the file only when a change is detected, and it minimizes I/O operations by eliminating the need for polling or repeated reads. The WatchService uses the underlying OS file system events (e.g., inotify on Linux, ReadDirectoryChanges on Windows) for efficient notification.

Answer

Read the file from disk every time it is accessed using Files.newInputStream()

Answer

Periodically check the file's lastModified timestamp using File.lastModified() and reload if changed

Answer

Read the file once at startup and cache the content in memory