1Z0-829 Practice Test 2 — 10 Questions

Question 1

An application deserializes objects from a network stream. To protect against deserialization attacks, which approach is most effective in Java 17?

Accepted Answer

Set an ObjectInputFilter on the ObjectInputStream. Setting an ObjectInputFilter on the ObjectInputStream allows you to define a filter that can reject deserialization of arbitrary or malicious classes, which is the primary defense against deserialization attacks. This mechanism, introduced in Java 9 and enhanced in later versions, lets you whitelist or blacklist classes based on patterns, limits on array sizes, or depth of object graphs, directly mitigating the risk of remote code execution or denial-of-service via crafted serialized data.

Answer

Declare all fields as transient

Answer

Use try-with-resources to auto-close the stream

Answer

Mark the class as final

Question 2

A company needs to read a large text file (over 2 GB) line by line in a Java application while minimizing memory footprint. Which approach is most efficient?

Accepted Answer

Use Files.lines(path) with try-with-resources. `Files.lines(path)` returns a `Stream<String>` that lazily reads lines from the file, processing them one at a time without loading the entire file into memory. Combined with try-with-resources, the underlying `BufferedReader` is automatically closed, ensuring efficient resource management even for files over 2 GB.

Answer

Use Files.readAllLines(path)

Answer

Use FileOutputStream with read() loop

Answer

Use Scanner with File and loop hasNextLine()

Question 3

A developer needs to ensure that a class `Shape` cannot be instantiated but can be extended. Which modifier should be used?

Accepted Answer

abstract. The `abstract` modifier is correct because an abstract class cannot be instantiated directly, but it can be extended by subclasses. This enforces the design intent that `Shape` serves as a base class for specific shapes like `Circle` or `Rectangle`, while preventing the creation of a generic `Shape` object.

Answer

private

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final

Answer

sealed

Question 4

A company uses a multi-release JAR (MR-JAR) that contains classes for Java 9 and Java 11 in `META-INF/versions/9/` and `META-INF/versions/11/` respectively. The application runs on Java 17. Which version of a class that exists in both versioned directories is loaded?

Accepted Answer

The version from META-INF/versions/11/. In a multi-release JAR (MR-JAR), the Java runtime selects the versioned directory that matches the major version of the running Java platform, or the highest versioned directory that does not exceed that version. Since the application runs on Java 17, and the highest available versioned directory is for Java 11 (META-INF/versions/11/), the class from that directory is loaded. The root directory is used only when no appropriate versioned directory exists.

Answer

The version from META-INF/versions/9/

Answer

The version from the root of the JAR

Answer

The version from META-INF/versions/17/

Question 5

A developer wants to copy all files from one directory to another, preserving file attributes (e.g., last modified time, permissions). Which NIO.2 method is most appropriate?

Accepted Answer

Files.copy(source, target, COPY_ATTRIBUTES). The `Files.copy(source, target, COPY_ATTRIBUTES)` method from the NIO.2 API copies the content of the file and, when the `COPY_ATTRIBUTES` option is specified, also preserves the file's metadata attributes such as last modified time, last access time, and permissions (where supported by the underlying file system). This option is specifically designed for copying with attribute preservation, making it the most appropriate choice for the developer's requirement.

Answer

Files.copy(source, target, REPLACE_EXISTING)

Answer

Files.move(source, target, ATOMIC_MOVE)

Answer

Files.walkFileTree() with a custom FileVisitor that copies files

Question 6

Which interface should be implemented to create a custom filter for deserialization in Java?

Accepted Answer

ObjectInputFilter. The `ObjectInputFilter` interface (introduced in Java 9) allows you to define a custom filter that validates classes and data being deserialized from an `ObjectInputStream`. By implementing this interface, you can reject potentially malicious or unexpected classes during deserialization, which is a key security measure against deserialization attacks.

Answer

Serializable

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ObjectOutput

Answer

FilterOutputStream

Question 7

You are developing a batch processing application that reads records from a CSV file and parses each row into an integer ID. The reading method readNextRecord() returns a String and can throw IOException and NumberFormatException. The method processID(int id) processes the ID. The entire process runs in a for loop over 10,000 records. The requirement is that if any record fails (either due to file read error or parsing), the loop must continue to the next record, but the exception must be logged for later review. Which approach best achieves this requirement?

Accepted Answer

Inside the loop, wrap the readNextRecord() and processID() calls in a try-catch block that catches IOException and NumberFormatException separately, logs the exception, and continues.. It places a try-catch block inside the loop that catches IOException and NumberFormatException separately, logs each exception, and then continues to the next iteration. This ensures that a failure in reading or parsing any single record does not terminate the loop, and each exception is logged individually for later review, meeting the requirement precisely.

Answer

Surround the entire loop with a try-catch block that catches IOException and NumberFormatException using multi-catch, logs once, and allows the loop to continue.

Answer

Inside the loop, wrap the calls in a try-catch that catches Exception, logs, and continues.

Answer

Declare the method to throw IOException and NumberFormatException and let the caller handle them.

Question 8

A developer creates a Java application that uses the new 'jpackage' tool to create an installer for Windows. The application is modular and has a main class declared in module-info. Which option is required to specify the main class when using jpackage?

Accepted Answer

--module. For a modular application with a main class declared in module-info, jpackage requires the `--module` option to specify the module name and, optionally, the main class (e.g., `--module com.example/com.example.Main`). This is because jpackage uses the module system to resolve the entry point, not a classpath or JAR-based approach.

Answer

-classpath

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--module-path

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--main-jar

Question 9

A developer needs to iterate over a List<String> and remove elements that are null. Which approach guarantees correct behavior without throwing a ConcurrentModificationException?

Accepted Answer

Use an Iterator explicitly and call its remove() method. Iterator.remove() is the safe and recommended way to remove elements during iteration, avoiding ConcurrentModificationException. Option A is incorrect because using list.remove() inside a for-each loop modifies the list directly while iterating, causing ConcurrentModificationException. Option B is incorrect because Stream.filter() does not modify the original list; it creates a new list, which may not meet the requirement to remove elements from the original. Option C is incorrect because although a decrementing for loop may work, it is error-prone and not the guaranteed approach; it is not the idiomatic Java solution.

Answer

Use a for-each loop and call list.remove() on the current element

Answer

Use a Stream's filter() method and collect the results

Answer

Use a traditional for loop with an index that decrements

Question 10

Match each JDBC type to its corresponding Java type.

Accepted Answer

VARCHAR: String. JDBC provides standard mappings from SQL types to Java types: VARCHAR to String, INTEGER to int, DATE to java.sql.Date, BLOB to java.sql.Blob, and CLOB to java.sql.Clob. Common confusions arise from mixing these mappings.

Answer

VARCHAR: java.sql.Date

Answer

INTEGER: String