1Z0-829 Practice Test 21 — 15 Questions

Question 1

Which TWO statements are true about ArrayList in Java 17? (Choose two.)

Accepted Answer

It implements the List interface. Option A is correct because java.util.ArrayList implements the java.util.List interface, giving it ordered, index-based access and allowing duplicates. Option D is correct because ArrayList extends java.util.AbstractList, which provides a skeletal implementation of the List interface and supplies much of the backing behavior for ArrayList. Option B is incorrect because ArrayList does not implement Set, which by contract forbids duplicate elements. Option C is incorrect because ArrayList does not implement Queue; Queue implementations include LinkedList, ArrayDeque, and PriorityQueue. Option E is incorrect because ArrayList is not synchronized; synchronization must be added externally, for example via Collections.synchronizedList, or by using CopyOnWriteArrayList.

Answer

It implements the Set interface

Answer

It implements the Queue interface

Answer

It is synchronized

Question 2

Which statement is true about the result of executing the jlink command shown in the exhibit?

Accepted Answer

It creates a runtime image containing the com.example.app module and its resolved dependencies.. The jlink command creates a custom runtime image that includes the specified module (com.example.app) and all of its resolved dependencies. It does not compile the module; compilation is done separately with javac. The resulting image is a directory structure with the JRE and module files, not a JAR.

Answer

It compiles the com.example.app module before creating the image.

Answer

It creates a runtime image that includes only the com.example.app module.

Answer

It creates a JAR file containing the com.example.app module.

Question 3

Given two named modules where module com.example.app requires module com.example.lib, which packages of com.example.lib are readable by com.example.app?

Accepted Answer

Only the packages exported by com.example.lib. In the Java module system, a module can only access packages from another module that are explicitly exported using the `exports` directive in the module's `module-info.java` file. Since `com.example.app` requires `com.example.lib`, only the packages exported by `com.example.lib` are readable; unexported packages remain encapsulated and inaccessible.

Answer

All packages except those explicitly concealed

Answer

All packages of com.example.lib

Answer

Only the packages opened by com.example.lib

Question 4

Which TWO of the following will sort a List<String> in natural (ascending) order?

Accepted Answer

list.sort(Comparator.naturalOrder());. Option A is correct because List.sort(Comparator) accepts a Comparator, and Comparator.naturalOrder() returns a comparator that orders elements according to their natural ordering, which for String is lexicographic ascending order. Option D is correct because Collections.sort(List) sorts the specified list into ascending order according to the natural ordering of its elements, which for String means lexicographic ascending order. Option B is incorrect because the lambda (a,b) -> b.compareTo(a) reverses the comparison, producing descending order. Option C is incorrect because Collections.reverseOrder() supplies a comparator that imposes the reverse of natural ordering, yielding descending order. Option E is incorrect because Arrays.sort(list) does not apply to a List<String>; Arrays.sort accepts arrays, not List instances, so it would not compile for this argument type.

Answer

list.sort((a,b) -> b.compareTo(a));

Answer

Collections.sort(list, Collections.reverseOrder());

Answer

Arrays.sort(list);

Question 5

Which three of the following are valid methods in the String class in Java 17? (Choose three.)

Accepted Answer

translateEscapes(). Option B, translateEscapes(), is a valid String method introduced in Java 15 that returns a new string with escape sequences (such as 
, 	, \) translated into their corresponding characters. Option C, toLowerCase(Locale), is a long-standing valid String method that converts all characters to lower case using the rules of the specified Locale. Option D, transform(Function<String, String>), is a valid String method added in Java 12 that applies the given function to the string and returns the function's result. Option A, substring(int, int, Locale), is not valid because the actual String.substring overloads take only integer arguments (substring(int) and substring(int, int)) and never a Locale. Option E, indent(String), is not valid because String.indent(int) takes an int number of spaces, not a String argument.

Answer

substring(int, int, Locale)

Answer

indent(String)

Question 6

Which TWO statements about creating custom exceptions are correct? (Choose two.)

Accepted Answer

It is good practice to provide a constructor that takes a String message and a Throwable cause.. Option D is correct because a well-designed custom exception should offer a constructor accepting a String message and a Throwable cause, allowing callers to preserve the original exception's stack trace and context via initCause/super. Option E is correct because Throwable's constructor Throwable(Throwable cause) sets the cause field directly, so calling super(cause) in a custom exception constructor automatically initializes the cause without needing an explicit initCause call. Option A is wrong because custom exceptions typically extend Exception (or RuntimeException) for application-level errors, not Error, which is reserved for serious JVM-level problems. Option B is wrong because there is no requirement or general best practice to declare custom exception classes final; subclassing is often allowed and useful. Option C is wrong because Exception is a class, not an interface, so custom exceptions extend it rather than implement it.

Answer

Custom exceptions should extend Error to indicate fatal errors.

Answer

Custom exception classes should be declared final to prevent subclassing.

Answer

Custom exceptions must implement the Exception interface.

Question 7

Given: outer: for(int i=0; i<3; i++) { for(int j=0; j<3; j++) { if(j==1) continue outer; } } How many times does the innermost loop body execute?

Accepted Answer

3. The outer loop runs with i=0,1,2. For each i, the inner loop starts j=0, executes the body once, then j=1 triggers 'continue outer', which skips the rest of the inner loop and increments i. Thus the inner loop body executes exactly once per outer iteration, for a total of 3 times.

Answer

0

Answer

9

Answer

6

Question 8

Which TWO statements are true regarding reading files with the NIO.2 API?

Accepted Answer

Files.newBufferedReader() provides buffered character input.. Option B is correct because Files.newBufferedReader(Path, Charset) returns a BufferedReader that reads characters through an internal buffer, which is the standard NIO.2 way to obtain buffered character input from a file. Option C is correct because Files.lines(Path) returns a lazily populated Stream that must be closed, so using it inside try-with-resources safely streams lines without loading the whole file into memory. Option A is wrong because Files.readAllLines() loads every line into a List in memory, which is not efficient for large files. Option D is wrong because Files.newInputStream() returns a plain InputStream (a SeekableByteChannel-based stream), not a FileChannel wrapper. Option E is wrong because Files.readAllBytes() reads the entire file into a single byte array, which is unsuitable for large binary files.

Answer

Files.readAllLines() is memory efficient for large files.

Answer

Files.newInputStream() wraps a FileChannel for high performance.

Answer

Files.readAllBytes() is the best choice for large binary files.

Question 9

Which three actions help secure a Java application that uses serialization? (Select three.)

Accepted Answer

Overriding resolveClass() in ObjectInputStream to validate class names.. Option A is correct because overriding resolveClass() in a custom ObjectInputStream lets you validate or whitelist class names before they are loaded during deserialization, blocking gadget-chain classes that attackers try to instantiate. Option B is correct because implementing ObjectInputFilter (or setting one via ObjectInputFilter.Config / ObjectInputStream.setObjectInputFilter) enforces a JEP 290 deserialization filter that rejects classes, array lengths, or graph depth outside an allowed range, which is the modern, recommended defense against deserialization attacks. Option C is correct because marking sensitive fields transient excludes them from the serialized byte stream, so secrets such as passwords or keys are never written out or restored during deserialization. Option D is not appropriate because SecureRandom is for generating unpredictable cryptographic values, not for serialVersionUID, which is only a version-compatibility identifier and need not be secret or random. Option E is not a security control: explicitly declaring serialVersionUID as a long constant only stabilizes version compatibility during deserialization and does nothing to prevent malicious class loading or data exposure.

Answer

Using SecureRandom to generate serialVersionUID.

Answer

Declaring serialVersionUID explicitly as a long constant.

Question 10

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

Accepted Answer

If both the try block and the close method throw exceptions, the close exception is suppressed.. Option B is correct because in try-with-resources, if the try block throws an exception and the automatic close() call also throws, the close exception is added to the original exception's suppressed exceptions list (retrievable via Throwable.getSuppressed()), so the try-block exception propagates as primary. Option D is correct because the resource declaration in try-with-resources requires the type to implement java.lang.AutoCloseable (which includes Closeable), since the compiler inserts a call to close() on each resource. Option A is wrong because resources are closed in the reverse order of their declaration, not the same order. Option C is wrong because multiple resources can be declared in one try-with-resources statement, separated by semicolons. Option E is wrong because resources are closed before any catch or finally block executes, as part of the implicit finally generated by the compiler.

Answer

Resources are closed in the order they are declared.

Answer

Only a single resource can be managed in a try-with-resources statement.

Answer

Resources are closed after the catch block if an exception occurs.

Question 11

Which TWO access modifiers can be applied to a top-level class in Java? (Choose two.)

Accepted Answer

package-private (no modifier). A top-level class in Java can be declared with the public modifier (option E), which makes the class accessible from any other package, and it can also be declared with no access modifier at all, i.e., package-private (option B), which restricts visibility to classes within the same package. These are the only two access levels the Java Language Specification permits for a top-level class, because a top-level type is always a member of a package rather than of another class. The static modifier (option A) is not an access modifier and is only meaningful for nested classes, methods, fields, and initializers, not for top-level types. The protected modifier (option C) and the private modifier (option D) are illegal on a top-level class since they only make sense for members enclosed within another class, where an enclosing type can control their visibility.

Answer

static

Answer

protected

Answer

private

Question 12

A class `Account` has a method `public void deposit(double amount)`. Which approach correctly demonstrates method overloading?

Accepted Answer

Adding a method `public void deposit(int amount)`. Method overloading requires methods to have the same name but different parameter lists. Changing the parameter type from `double` to `int` satisfies this requirement, allowing the compiler to distinguish the methods at compile time based on the argument type.

Answer

Adding a method `public void deposit(double amount)` with different implementation

Answer

Adding a method `public int deposit(double amount)`

Answer

Adding a method `protected void deposit(double amount)`

Question 13

Which two statements are true about the peek method of the Stream API? (Choose two.)

Accepted Answer

It is primarily used for debugging purposes.. Option A is correct because Stream.peek(Consumer) is designed mainly for debugging: it lets you inspect elements as they flow through the pipeline without altering the stream's result. Option B is correct because peek is an intermediate operation that returns a new Stream, so it is lazy and only executes when a terminal operation is invoked. Option C is not correct because peek's Consumer should not mutate stream elements; doing so is discouraged and can produce unpredictable results. Option D is not correct because peek is not a terminal operation—it does not trigger pipeline execution by itself. Option E is not correct because peek does not transform elements into new values; that is the role of map.

Answer

It can be used to modify the elements of the stream.

Answer

It is a terminal operation.

Answer

It can be used to transform the elements into a new value.

Question 14

A team has a multi-release JAR that supports both Java 11 and Java 17. They want to ensure that when running on Java 17, the version-specific classes in META-INF/versions/17 are used. Which condition must be true?

Accepted Answer

The manifest must contain 'Multi-Release: true'. The Java runtime checks for the `Multi-Release: true` entry in the JAR's manifest file to enable multi-release JAR functionality. Without this manifest attribute, the JVM ignores versioned directories under `META-INF/versions/` and uses only the root classes, even if the JAR was compiled with `--multi-release 17`.

Answer

The JAR must have a module-info.class in the root

Answer

The JAR must be placed on the module path

Answer

The JAR must be created using the --multi-release 17 option

Question 15

Which TWO statements about Java serialization are true?

Accepted Answer

During deserialization, the constructor of the serialized class is not invoked.. Option B is correct because Java deserialization reconstructs objects from the byte stream by allocating the object via the JVM without calling any constructor of the serializable class (constructors of non-serializable superclasses are invoked, but the class's own constructor is not). Option D is correct because serialization captures the state of an object's instance fields, and static fields belong to the class rather than to any instance, so they are never written to the stream. Option A is wrong because serialVersionUID is optional; if not declared, the JVM computes one automatically from the class structure, though explicit declaration is recommended. Option C is wrong because Externalizable extends Serializable, so an Externalizable class is already Serializable and must implement writeExternal and readExternal. Option E is wrong because transient fields are explicitly excluded from serialization and are restored to their default values (e.g., null, 0, false) after deserialization.

Answer

The serialVersionUID must be explicitly declared in every serializable class.

Answer

A class that implements Externalizable does not need to implement Serializable.

Answer

Fields marked as transient are serialized by default.