1Z0-829 Practice Test 35 — 15 Questions

Question 1

Refer to the exhibit. Two Java classes are defined as shown. What is the output when the Sub class is executed?

Accepted Answer

World. The Sub class overrides the print() method from Super and does not call super.print(). Therefore, when Sub's print() is executed, it only prints "World" without printing "Hello". The output is simply "World".

Answer

HelloWorld

Answer

Hello

Answer

No output (compilation error)

Question 2

A large-scale data processing platform uses Java to read and write files across multiple nodes. Recently, operations have slowed down significantly. The system uses FileInputStream and FileOutputStream wrapped in BufferedInputStream and BufferedOutputStream with default buffer sizes (8 KB). The operations team suspects that the default buffer size is causing excessive system calls. The files are typically 100 MB to 1 GB in size. Which change would most improve I/O performance while minimizing memory overhead?

Accepted Answer

Increase the buffer size to 64 KB.. Increasing the buffer size to 64 KB reduces the number of system calls (read/write) by allowing more data to be transferred per call. With default 8 KB buffers and 100 MB–1 GB files, the overhead of frequent kernel transitions is significant. A 64 KB buffer strikes a good balance between performance gain and memory overhead, as it is large enough to reduce syscalls substantially without consuming excessive heap space.

Answer

Switch to using FileChannel with direct ByteBuffers for all file operations.

Answer

Use memory-mapped files (MappedByteBuffer) for the entire file.

Answer

Replace FileInputStream with FileReader and FileOutputStream with FileWriter.

Question 3

You are developing a microservice that processes financial transactions. The service reads transaction data from a message queue, validates it, and writes results to a database. The code uses a try-with-resources statement to manage database connections. During testing, you notice that when a transaction fails validation, the service throws an IllegalStateException before closing the database connection, causing a resource leak. You need to ensure that the database connection is always closed properly, even if an exception is thrown during validation. The current code structure is:

try (Connection conn = DriverManager.getConnection(url, user, pass)) {
    // read from queue
    // validate transaction
    // if invalid, throw new IllegalStateException("Invalid transaction");
    // write to database
}

Which course of action would you recommend?

Accepted Answer

No change is needed; the try-with-resources ensures the connection is closed.. Try-with-resources automatically closes any resource that implements AutoCloseable (including Connection) when the try block exits, whether normally or via an exception. The IllegalStateException thrown during validation does not prevent the connection from being closed; the close() method is called as part of the implicit finally block generated by the compiler.

Answer

Move the connection creation outside the try-with-resources to manually manage it.

Answer

Replace the try-with-resources with a try-catch-finally block and close the connection in the finally block.

Answer

Add a catch block to catch the IllegalStateException and close the connection.

Question 4

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

Accepted Answer

0. (0) because the `break outer` statement immediately terminates the outer `while` loop when `j` equals 1 during the first iteration of the inner `for` loop. Since `i` is incremented only after the inner loop completes, and the inner loop never finishes its first iteration, `i` remains 0.

Answer

1

Answer

2

Answer

3

Question 5

Which TWO statements about module descriptors are true?

Accepted Answer

A module descriptor can use the opens keyword to enable deep reflection on specific packages.. The `opens` keyword in a module descriptor (module-info.java) allows deep reflection (access to private members) on specific packages at runtime, which is necessary for frameworks like Hibernate or JPA that rely on reflection. Option E is correct because the `transitive` keyword is used only within `requires` directives to indicate that any module that requires the current module also implicitly requires the specified module.

Answer

A module descriptor can use the provides keyword to declare that it uses a service.

Answer

A module descriptor must require the java.base module explicitly.

Answer

A module descriptor can specify which packages are exported with the export keyword.

Question 6

Given: Map map = new HashMap<>(); map.put("A", 1); map.put("B", 2); map.merge("A", 3, (v1, v2) -> v1 + v2); System.out.println(map.get("A")); What is the result?

Accepted Answer

4. (4) because the `merge` method on a Map associates the key "A" with the result of applying the remapping function `(v1, v2) -> v1 + v2` to the current value (1) and the given value (3), producing 1 + 3 = 4. If the key had been absent, the new value would be 3, but since it is present, the function is invoked and the result replaces the old value.

Answer

1

Answer

3

Answer

null

Question 7

Which TWO statements about method references are true? (Choose two.)

Accepted Answer

Constructor references use the syntax Class::new.. Constructor references use the syntax `Class::new` to refer to a constructor of a class, which can be used with a functional interface whose method matches the constructor's signature. This allows creating instances without explicitly invoking `new`, leveraging the same target type inference as lambda expressions.

Answer

Array constructor references are not supported.

Answer

Instance method references always use the keyword static.

Answer

Method references cannot refer to methods declared in the same class.

Question 8

A developer needs to read a large text file (several gigabytes) line by line as efficiently as possible, processing each line without loading the entire file into memory. Which approach should the developer use?

Accepted Answer

Use Files.lines with a try-with-resources block, and process each line using the stream.. `Files.lines` returns a `Stream<String>` that lazily reads lines from the file, processing them one at a time without loading the entire file into memory. The try-with-resources block ensures the underlying file handle is closed automatically, preventing resource leaks. This approach is specifically designed for efficient, memory-safe line-by-line processing of large files.

Answer

Use a FileReader wrapped in a BufferedReader, and process each line in a loop.

Answer

Use a FileInputStream to read bytes, then manually parse newline characters.

Answer

Use Files.readAllLines to read the entire file into a List<String> and then iterate.

Question 9

Given the code snippet: List list = new ArrayList<>(List.of("A","B","C")); list.add("D"); System.out.println(list.size()); What is the result?

Accepted Answer

4. The code creates an ArrayList from a fixed-size list returned by List.of() using the ArrayList constructor, which creates a new mutable list containing the elements "A", "B", "C". The subsequent call to list.add("D") successfully appends the element, resulting in a list of size 4. The ArrayList constructor copies the elements, so the original immutable list is not modified.

Answer

5

Answer

UnsupportedOperationException

Answer

Compilation fails

Answer

3

Question 10

What is the cause of the ClassCastException?

Accepted Answer

The value stored is Integer but retrieved as String.. The ClassCastException occurs because the code retrieves a value from the store map and attempts to cast it to String, but the actual stored object is an Integer. Since the map is not using generics (raw type), the compiler does not enforce type safety, allowing the mismatch to be caught only at runtime.

Answer

The store map is not type-safe.

Answer

The get method should use (T) cast instead of type.cast().

Answer

The type parameter T is not used correctly.

Question 11

Which statement about the code is correct?

Accepted Answer

A compilation error occurs in the Triangle class because Triangle is not listed in the permits clause.. In a sealed class hierarchy, the `permits` clause must list all direct subclasses. If `Triangle` extends `Shape` but is not listed in the `permits` clause of `Shape`, the compiler will report an error. The sealed class mechanism enforces that only explicitly permitted subclasses may extend the sealed class.

Answer

A compilation error occurs because Circle must be declared final.

Answer

A compilation error occurs because Shape must be declared abstract.

Answer

The code compiles successfully.

Question 12

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 13

Which TWO statements are true about the Java module system?

Accepted Answer

The --add-exports flag can be used to export a package from one module to a specific target module.. The --add-exports command-line flag allows you to export a package from one module to a specific target module at runtime, overriding the module system's encapsulation. This is useful for modules that do not export a package by default but need to be accessed by a specific module during development or testing.

Answer

The --add-exports command-line flag opens a package for deep reflection.

Answer

The jlink tool can generate module-info.java files for automatic modules.

Answer

The exports directive can be used to export a specific class to another module.

Question 14

Which Map implementation guarantees that keys are sorted in their natural order?

Accepted Answer

TreeMap. TreeMap implements the SortedMap interface, which ensures that keys are stored in their natural ordering (as defined by Comparable) or by a provided Comparator. This makes TreeMap the only standard Map implementation that guarantees sorted keys without external sorting.

Answer

Hashtable

Answer

LinkedHashMap

Answer

HashMap

Question 15

What is the output of the program?

Accepted Answer

[A, B, C]. The program code was not provided in the question. Without the code, it is impossible to determine the output. Therefore, none of the options can be confirmed as correct.

Answer

[A, B, C, D]

Answer

[A, B, D]

Answer

[B, C, D]