1Z0-829 Practice Test 5 — 25 Questions

Question 1

A developer needs to parse a date string '2024-07-04' into a LocalDate object. Which approach is correct?

Accepted Answer

LocalDate.parse("2024-07-04"). `LocalDate.parse("2024-07-04")` uses the default ISO-8601 format (yyyy-MM-dd), which matches the given string exactly. The `LocalDate` class provides a static `parse` method that returns a `LocalDate` object without needing an explicit formatter when the input follows the standard pattern.

Answer

LocalDate.of(2024, 07, 04)

Answer

DateFormat.getDateInstance().parse("2024-07-04")

Answer

new LocalDate(2024, 7, 4)

Question 2

Given: var list = List.of("A", "B", "C"); list.set(0, "Z"); What is the result?

Accepted Answer

An UnsupportedOperationException is thrown. The `List.of()` method returns an immutable list, meaning its elements cannot be added, removed, or replaced. Calling `set()` on an immutable list throws an `UnsupportedOperationException` at runtime, which is why option B is correct.

Answer

An ArrayIndexOutOfBoundsException is thrown

Answer

The code does not compile because var cannot be used with List.of

Answer

The list is modified to [Z, B, C]

Question 3

The code fails to compile. What is the reason?

Accepted Answer

The flatMap method requires a function that returns a Stream, but String::chars returns an IntStream.. The `chars()` method on `String` returns an `IntStream`, not a `Stream`. The `flatMap` method on a `Stream` expects a function that returns a `Stream`, but `String::chars` returns an `IntStream`, which is a primitive stream and not a subtype of `Stream`. This type mismatch causes a compilation error.

Answer

The collect method is not applicable for a Stream<Character>.

Answer

The method reference String::chars is not a valid method reference.

Answer

The chars() method returns a Stream, but flatMap requires a function that returns a Stream.

Question 4

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 5

Refer to the exhibit. A developer runs the code and gets an IllegalStateException on the second forEach. Which statement explains why?

Accepted Answer

The stream has already been operated upon or closed.. A Stream in Java cannot be reused after a terminal operation has been executed. Once the first forEach terminal operation completes, the stream is consumed and closed. Attempting to call another terminal operation (the second forEach) on the same stream reference throws an IllegalStateException with the message 'stream has already been operated upon or closed'.

Answer

The filter operation is not lazy.

Answer

The map operation modifies the source list.

Answer

The stream is not closed after the first terminal operation.

Question 6

A developer needs to write text to a file with UTF-8 encoding. Which class should be used?

Accepted Answer

new OutputStreamWriter(new FileOutputStream(file), StandardCharsets.UTF_8). It explicitly constructs an OutputStreamWriter with a FileOutputStream and StandardCharsets.UTF_8, ensuring the text is written with UTF-8 encoding. This is the standard approach when you need precise control over the character encoding, as the OutputStreamWriter acts as a bridge from byte streams to character streams using the specified charset.

Answer

BufferedWriter

Answer

FileWriter

Answer

PrintWriter with default constructor

Question 7

Given: HashSet set = new HashSet<>(); set.add("A"); set.add("B"); set.add("C"); set.add("A"); System.out.println(set.size()); What is the output?

Accepted Answer

3. HashSet does not allow duplicate elements. When adding "A" twice, the second add is ignored, so the set contains only three unique elements: "A", "B", and "C". Therefore, set.size() returns 3.

Answer

Compilation fails

Answer

4

Answer

2

Question 8

A developer wants to find the longest word in a list of strings. Which stream operation should be used?

Accepted Answer

stream().max(Comparator.comparingInt(String::length)). The `max()` terminal operation, when combined with a `Comparator` that compares strings by their length, returns the longest word in the stream. The `max()` operation uses the provided comparator to determine the 'largest' element according to the ordering, which in this case is the string with the greatest length.

Answer

stream().sorted(Comparator.comparingInt(String::length).reversed()).findFirst()

Answer

stream().min(Comparator.comparingInt(String::length))

Answer

stream().sorted(Comparator.comparingInt(String::length)).findFirst()

Question 9

You are a software architect at a financial firm. Your team is developing a modular Java 17 application that comprises several modules: 'com.bank.core' (provides core banking services), 'com.bank.web' (REST API), and 'com.bank.persistence' (database access). The application uses the 'java.sql' module for JDBC and 'java.logging' for logging. The team uses Maven for dependency management. The application has an external dependency on the 'com.fasterxml.jackson.databind' library (Jackson) for JSON processing, which is provided as a non-modular jar. The Jackson jar is placed on the module path. The application modules are all named modules with module-info files. At runtime, the 'com.bank.web' module requires 'com.bank.core' and 'com.fasterxml.jackson.databind' (the automatic module). The 'com.bank.core' module requires 'java.sql' and 'java.logging'. When the application runs, it throws an 'IllegalAccessError' indicating that the module 'com.bank.core' tries to access a class from 'com.fasterxml.jackson.databind' but the module does not read it. Yet, 'com.bank.web' is the only module that explicitly requires Jackson. What is the most likely cause and the correct resolution?

Accepted Answer

Add 'requires com.fasterxml.jackson.databind' to the module-info.java of 'com.bank.core' because it uses Jackson classes directly.. The error indicates that 'com.bank.core' directly uses classes from 'com.fasterxml.jackson.databind', but its module-info.java does not include a 'requires com.fasterxml.jackson.databind' directive. In the Java module system, a module can only access types from another module if it explicitly reads that module. Since 'com.bank.core' needs Jackson classes at runtime, it must declare the dependency itself, even if another module ('com.bank.web') also requires it.

Answer

Convert all application modules to unnamed modules by removing module-info files.

Answer

Place the Jackson jar on the classpath instead of the module path.

Answer

Use jlink to create a custom runtime image including all modules and the Jackson jar.

Question 10

Which TWO statements about try-with-resources are correct? (Choose two.)

Accepted Answer

Resources are closed in the reverse order of their declaration.. Option A is correct because try-with-resources closes resources in the reverse order of their declaration, i.e., the last resource declared is closed first, mirroring a stack-like LIFO teardown. Option E is correct because if the try block throws an exception and a resource's close() method also throws, the try block's exception is the one that propagates while the close() exception is attached to it via addSuppressed(), retrievable with getSuppressed(). Option B is wrong because it states the opposite ordering (same order as declaration) rather than the required reverse order. Option C is wrong because resources need not implement java.io.Closeable specifically; they may implement java.lang.AutoCloseable, which is broader and includes Closeable as a subinterface. Option D is wrong because it claims earlier-declared resources close first, which contradicts the reverse-order rule.

Answer

Resources are closed in the same order as their declaration.

Answer

Resources declared in try-with-resources must implement the Closeable interface.

Answer

Resources declared earlier in the try clause are closed first.

Question 11

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

Accepted Answer

1 3 5 7 9. The loop iterates from 0 to 9, and the `continue` statement skips the rest of the loop body when the condition `i % 2 == 0` is true (i.e., for even numbers). Only odd numbers (1, 3, 5, 7, 9) are printed, each followed by a space.

Answer

No output

Answer

0 2 4 6 8

Answer

0 1 2 3 4 5 6 7 8 9

Question 12

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. 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

Question 13

Which code will successfully produce an Optional<Integer> that contains the maximum value from a list of integers?

Accepted Answer

B and D both produce Optional.. It states that options B and D both produce Optional. Option B uses list.stream().collect(Collectors.maxBy(Integer::compareTo)), which returns an Optional containing the maximum element. Option D uses list.stream().max(Integer::compareTo), which also returns an Optional with the maximum element. Option C, list.stream().max() without arguments, fails to compile because the Stream.max() method requires a Comparator. Therefore, A is the correct choice.

Answer

list.stream().collect(Collectors.maxBy(Integer::compareTo))

Answer

list.stream().max()

Answer

list.stream().max(Integer::compareTo)

Question 14

Consider the following do-while loop:

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

What is printed?

Accepted Answer

3. The do-while loop executes the body first (x--), then checks the condition x < 10. After the first iteration, x becomes 9, and the condition (9 < 10) is true. As x continues to decrease, it will always be less than 10, so the condition remains true forever. This results in an infinite loop; the program never reaches the print statement. Therefore, no output is produced, and none of the options (3, 2, 1) are correct.

Answer

The loop does not compile because x is not declared final.

Answer

2

Answer

1

Question 15

Refer to the exhibit. Given the following code:

```java
1: sealed interface Shape permits Circle { }
...
10: class Circle implements Shape { }
```

What is the result?

Accepted Answer

Compilation fails at line 10. In Java 17, when a sealed interface (like `Shape`) declares a `permits` clause listing permitted subclasses (e.g., `Circle`), each permitted subclass must explicitly declare itself as `sealed`, `non-sealed`, or `final`. If the `Circle` class is defined as `class Circle implements Shape` without any of these modifiers, compilation fails at line 10 where that class is defined. The error is that the class is not allowed to extend/implement the sealed interface unless it has the required modifier.

Answer

Compilation fails due to missing permits in Circle

Answer

Runtime exception

Answer

Compilation succeeds

Question 16

Arrange the steps to create a custom exception class in Java in the correct order.

Accepted Answer

1. Define a class that extends Exception or RuntimeException. 2. Add constructors (default, with message, with cause). 3. Optionally override methods like getMessage() or toString().. Custom exceptions extend Exception (checked) or RuntimeException (unchecked). Constructors typically call super(message) or super(cause).

Answer

1. Add constructors (default, with message, with cause). 2. Define a class that extends Exception or RuntimeException. 3. Optionally override methods.

Answer

1. Define a class (without extending Exception or RuntimeException). 2. Add constructors that call super(message). 3. Optionally override methods.

Answer

1. Override methods like getMessage() or toString(). 2. Define a class extending Exception or RuntimeException. 3. Add constructors.

Question 17

Arrange the steps to create and use a generic method in Java.

Accepted Answer

Declare the method with a type parameter in angle brackets before the return type, then use the type parameter for parameters and return type, then implement the method body using the type parameter, then invoke the method either with explicit type argument or type inference.. Generic methods allow type-safe operations on different types. The type parameter is placed before the return type.

Answer

Write the method body first using a specific type, then replace the specific type with a type parameter, then add the type parameter declaration in the method signature, then call the method with the specific type.

Answer

Declare the method with a type parameter after the return type, then use the type parameter in the method body, then call the method with type inference.

Answer

Use a wildcard (?) in the method signature instead of a type parameter, then implement the method body, then call the method with different types.

Question 18

What is the output of the following code?

List<Integer> list = List.of(0, 1, 2, 3);
System.out.println(list.indexOf(0) + " " + list.lastIndexOf(3));

Accepted Answer

0 3. The list is [0, 1, 2, 3]. The indexOf(0) returns 0 because 0 is at index 0. The lastIndexOf(3) returns 3 because 3 is at index 3. The output is "0 3".

Answer

0 2

Answer

1 2

Answer

1 3

Question 19

Refer to the exhibit. What is the output when the program is executed?

Accepted Answer

0 0 0 1 0 2 1 0 1 1. The code uses nested for loops with break labels. The outer loop iterates i from 0 to 2, and the inner loop iterates j from 0 to 2. When i == 1 and j == 1, the break outer; statement exits both loops, so after printing 0 0, 0 1, 0 2, 1 0, 1 1, the program terminates. This matches option C.

Answer

0 0 0 1 0 2 1 0 1 1 1 2

Answer

0 0 0 1 0 2 1 0 1 1 2 0 2 1 2 2

Answer

0 0 0 1 0 2 1 0 1 1 1 2 2 0 2 1 2 2

Question 20

Which TWO statements are true about the sealed class feature in Java 17?

Accepted Answer

A sealed class restricts which other classes or interfaces may extend or implement it.. Option A is correct because the core purpose of the sealed class feature introduced in Java 17 is to restrict which other classes or interfaces may extend or implement it, using the permits clause to name the allowed direct subtypes. Option C is correct because any permitted subclass of a sealed class (or subinterface of a sealed interface) must itself be declared as final, sealed, or non-sealed, ensuring the hierarchy remains controlled and exhaustively known. Option B is wrong because a sealed interface can absolutely use a permits clause to specify its permitted implementing classes or extending interfaces. Option D is wrong because the permits clause lists only the permitted direct subclasses, and it may be omitted entirely when the subclasses are declared in the same source file. Option E is wrong because a sealed class need not be abstract; it can be concrete, and sealing is independent of abstractness.

Answer

A sealed interface cannot use the permits clause.

Answer

The permits clause must list all direct subclasses of a sealed class.

Answer

A sealed class must be declared as abstract.