1Z0-829 Practice Test 7 — 10 Questions

Question 1

Which of the following lambda expressions is syntactically invalid?

Accepted Answer

(a, b) -> return a + b;. Syntactically invalid because in a lambda expression, the `return` keyword is only allowed inside a block body (with braces). When using an expression body (no braces), the `return` keyword must be omitted, and the expression itself is implicitly returned. Option C incorrectly uses `return` without braces, which is a syntax error.

Answer

() -> {return 42;}

Answer

(a, b) -> a + b

Answer

(int a, int b) -> a + b

Answer

(a) -> a * 2

Question 2

A developer creates an unmodifiable list via Collections.unmodifiableList(originalList). Later, originalList is modified by adding an element. Which statement is true?

Accepted Answer

The unmodifiable list reflects the addition. D is correct because `Collections.unmodifiableList()` returns a view-backed unmodifiable list that reflects any changes made to the original list. The unmodifiable list does not create a snapshot; it wraps the original list, so modifications to the original are visible through the unmodifiable wrapper.

Answer

The unmodifiable list remains unchanged

Answer

The unmodifiable list becomes inconsistent

Answer

An UnsupportedOperationException is thrown

Question 3

Which two statements about the java.time.Duration class are true? (Choose two.)

Accepted Answer

Duration can be negative.. Option B is correct because java.time.Duration models an amount of time in terms of seconds and nanoseconds, and both components may carry a negative sign, so a Duration can represent a negative span (e.g., Duration.ofSeconds(-5) or the result of between() when the end is before the start). Option C is correct because Duration is a final, immutable value-based class: all its fields are final and every mutating-looking method such as plus() or withSeconds() returns a new instance, which makes instances safe to share across threads without synchronization. Option A is wrong because Duration only supports time-based units (days treated as exactly 24 hours, hours, minutes, seconds, nanos); months and years are date-based and are handled by java.time.Period. Option D is wrong because Duration.between() requires two Temporal objects that support time-based fields, and LocalDate is date-only, so passing LocalDate arguments throws an UnsupportedTemporalTypeException (or fails to compile against the Temporal signature). Option E is wrong because Duration's internal representation is seconds plus a nanosecond adjustment, not a days-based representation; the days-based model belongs to Period.

Answer

Duration supports units like months and years.

Answer

Duration.between(LocalDate.now(), LocalDate.now()) returns a Duration.

Answer

Duration uses a days-based representation.

Question 4

A web application allows users to specify filenames for uploaded documents. The application saves files to a directory using the provided name. Which secure programming practice should be applied to prevent path traversal attacks?

Accepted Answer

Use File.getCanonicalPath() to resolve the path and check it starts with the intended directory.. `File.getCanonicalPath()` resolves all symbolic links, `.` and `..` sequences, and platform-specific path conventions to produce an absolute, unique path. By then verifying that this canonical path starts with the intended base directory (e.g., `/var/uploads/`), the application can definitively reject any path that escapes outside the allowed directory, even if the user-supplied filename contains encoded or obfuscated traversal sequences.

Answer

Validate that the filename contains only alphanumeric characters.

Answer

Generate a random UUID for each file, ignoring the user-provided filename.

Answer

Replace all occurrences of ".." and "/" with an empty string.

Question 5

Which of the following is a terminal operation of the Stream API?

Accepted Answer

forEach(). (forEach()) is correct because it is a terminal operation in the Stream API. Terminal operations produce a result or side effect and close the stream, meaning no further operations can be performed on the same stream. forEach() consumes each element of the stream and returns void, making it a terminal operation.

Answer

map()

Answer

filter()

Answer

peek()

Question 6

A team uses a TreeSet with a custom Comparable that returns 0 for objects that are not logically equal (e.g., based on one field but objects differ in another). What is the likely outcome when adding such objects?

Accepted Answer

The second object is not added because TreeSet considers it a duplicate. TreeSet uses the compareTo() method of the Comparable interface (or Comparator) to determine ordering and equality. When compareTo() returns 0 for two objects that are not logically equal (e.g., they share the same field used in comparison but differ in other fields), TreeSet treats them as duplicates and does not add the second object. This is because TreeSet relies on the comparison result, not the equals() method, for uniqueness.

Answer

The second object replaces the first

Answer

A ClassCastException is thrown

Answer

Both objects are added and insertion order is preserved

Question 7

Which of the following correctly uses try-with-resources to ensure a FileInputStream is closed after use?

Accepted Answer

try (FileInputStream fis = new FileInputStream("file.txt")) { ... }. It uses the try-with-resources syntax (try (resource declaration) { ... }), which automatically closes the FileInputStream when the block exits, regardless of exceptions. This ensures the resource is closed without requiring an explicit finally block, as mandated by the AutoCloseable interface.

Answer

FileInputStream fis = new FileInputStream("file.txt"); try { ... } finally { fis.close(); }

Answer

try { FileInputStream fis = new FileInputStream("file.txt"); ... } finally { fis.close(); }

Answer

try (fis = new FileInputStream("file.txt")) { ... }

Question 8

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 9

A junior developer writes a method that uses a switch statement to handle different types of user input. The input is an integer representing an operation code. The developer uses a traditional switch statement with break statements. However, when operation code 2 is entered, the program also executes the code for operation 3. What is the most likely cause?

Accepted Answer

The break statement is missing after the operation 2 case.. In a traditional Java switch statement, execution continues into the next case block unless a break statement is encountered. If operation code 2 executes the code for operation 3, it indicates that the break statement is missing after the case for operation 2, causing fall-through to the next case.

Answer

The operation codes are not mutually exclusive.

Answer

The variable is being modified inside the switch.

Answer

The switch statement uses fall-through by design.