1Z0-829 Practice Questions 1 — 50 Questions

Question 1

What does the Map.merge() method do if the specified key is absent?

Accepted Answer

Associates the key with the given value. When the specified key is absent in the map, the `Map.merge()` method associates the key with the given value without invoking the remapping function. This is specified in the Java API documentation: if the key is not present (or maps to null), the key is associated with the given non-null value.

Answer

Calls the remapping function with null and the value

Answer

Throws NullPointerException

Answer

Removes the key if present

Question 2

A developer is designing a service that processes multiple files concurrently. To avoid resource leaks, which practice is essential?

Accepted Answer

Use try-with-resources for each AutoCloseable resource. Try-with-resources guarantees that each AutoCloseable resource is closed automatically at the end of the statement, even if an exception occurs. This is essential when processing multiple files concurrently, as it prevents resource leaks without requiring explicit close() calls in finally blocks.

Answer

Ensure each thread has its own copy of the file handle

Answer

Call close() on each stream in a separate try-catch block

Answer

Use FileLock to prevent concurrent access

Question 3

A developer runs the command above on a JAR file. Which statement accurately describes the module myapp?

Accepted Answer

The module exports com.myapp.internal to the module myapp.tests only.. The command `java --describe-module myapp` outputs the module descriptor, which includes `exports com.myapp.internal to myapp.tests`. This indicates that the module `myapp` exports the package `com.myapp.internal` specifically to the module `myapp.tests` only, not to all modules. The `exports ... to` syntax restricts access to a qualified list of modules.

Answer

The module opens com.myapp.internal for deep reflection to all modules.

Answer

The module provides a service implementation.

Answer

The module requires java.base explicitly; it is not mandated.

Question 4

Which TWO statements about lambda expressions are true? (Choose two.)
A. A lambda expression can be assigned to a functional interface variable.
B. A lambda expression can access final or effectively final local variables.
C. A lambda expression can throw any checked exception.
D. A lambda expression can be used to create an instance of an abstract class.
E. A lambda expression can be used to implement multiple abstract methods.

Accepted Answer

A lambda expression can be assigned to a functional interface variable.. False: A lambda expression can only throw checked exceptions that are declared in the functional interface's abstract method, not any checked exception. Options B and C are true: a lambda can be assigned to a functional interface variable, and it can access final or effectively final local variables. Option D is false: a lambda can only implement one abstract method (functional interface). Option E is false: lambdas cannot instantiate abstract classes; they only implement functional interfaces.

Answer

A lambda expression can throw any checked exception.

Answer

A lambda expression can be used to implement multiple abstract methods.

Answer

A lambda expression can be used to create an instance of an abstract class.

Question 5

Which THREE of the following are true about the Optional class? (Choose three.)

Accepted Answer

Optional.empty().orElseThrow(IllegalStateException::new) throws IllegalStateException. `Optional.empty().orElseThrow(IllegalStateException::new)` explicitly throws a new `IllegalStateException` when the Optional is empty. The `orElseThrow` method is designed to throw the provided exception supplier's exception if no value is present.

Answer

Optional.of(null) returns an empty Optional

Answer

Optional.get() on empty Optional returns null

Question 6

Given the following switch statement:

```java
int x = 2;
switch (x) {
    default:
        System.out.print("default ");
    case 1:
        System.out.print("1 ");
    case 2:
        System.out.print("2 ");
    case 3:
        System.out.print("3 ");
        break;
    case 4:
        System.out.print("4 ");
}
```

What is the output?

Accepted Answer

2 3. The switch statement starts execution at the matching case (case 2) and then falls through to subsequent cases until a break statement is encountered. Since case 2 has no break, it prints "2 ", then falls through to case 3, prints "3 ", and the break terminates the switch. The default case is not executed because a matching case was found before it.

Answer

2

Answer

2 3 4

Answer

default 1 2 3

Question 7

A developer needs to read all lines from a text file named "data.txt" that uses UTF-8 encoding. Which code correctly reads the file using the NIO.2 API?

Accepted Answer

Files.readAllLines(Path.of("data.txt"), StandardCharsets.UTF_8). `Files.readAllLines()` reads all lines from a file into a `List<String>`, and it accepts a `Path` and a `Charset` (here `StandardCharsets.UTF_8`) to handle encoding. This method is part of the NIO.2 API and directly fulfills the requirement to read all lines from a UTF-8 encoded file.

Answer

Files.lines(Path.of("data.txt"), StandardCharsets.UTF_8).collect(Collectors.toList())

Answer

Files.readString(Path.of("data.txt"), StandardCharsets.UTF_8)

Answer

Files.readAllBytes(Path.of("data.txt")).toString()

Question 8

What does the following code print? List list = new ArrayList<>(List.of(1,2,3)); list.replaceAll(x -> x * 2); System.out.println(list);

Accepted Answer

[2,4,6]. The `replaceAll` method on a `List` applies the given `UnaryOperator` to each element, replacing it with the result. Here, `x -> x * 2` multiplies each integer by 2, so the list becomes `[2, 4, 6]`. Option B is correct because the code compiles and runs, producing that output.

Answer

[2,3,4]

Answer

Compilation fails

Answer

[1,4,9]

Answer

[1,2,3]

Question 9

Consider the following code:

```java
boolean a = true, b = false, c = false;
if (a && b || c) {
    System.out.println("True");
} else {
    System.out.println("False");
}
```

What is the output?

Accepted Answer

False. The expression `a && b || c` evaluates as `(a && b) || c` due to operator precedence (`&&` has higher precedence than `||`). With `a=true`, `b=false`, `c=false`, `(true && false)` is `false`, then `false || false` is `false`, so the `else` branch prints "False". Option B is correct.

Answer

The code does not compile because of invalid boolean expression.

Answer

The output cannot be determined without runtime values.

Answer

True

Question 10

Refer to the exhibit. The exhibit shows a code snippet. What is the output when the variable day is set to Day.WEDNESDAY?

Accepted Answer

9. (9) because the switch statement on Day.WEDNESDAY (ordinal 2) does not have break statements for cases WEDNESDAY, THURSDAY, FRIDAY, and SATURDAY, causing fall-through. Execution adds values: WEDNESDAY (3), THURSDAY (4), FRIDAY (5), SATURDAY (6), totaling 18. Then the default case subtracts 9, resulting in 9.

Answer

7

Answer

Compilation error

Answer

6

Question 11

Which of the following will compile without error and produce an unmodifiable list containing three elements?

Accepted Answer

List.of("A","B","C"). `List.of("A","B","C")` returns an unmodifiable list exactly as required. In Java 9+, `List.of` returns an immutable list; any attempt to modify it throws `UnsupportedOperationException`. Option A, `Arrays.asList`, returns a fixed-size list backed by an array that allows modification via `set()`, so it is not unmodifiable. Option B, `new ArrayList<>(List.of(...))`, creates a mutable ArrayList. Option D, `Collections.unmodifiableList`, returns an unmodifiable view, but the underlying ArrayList is still mutable; modifications to the original list affect the view, so it does not guarantee immutability. Therefore, only C meets the criteria.

Answer

Arrays.asList("A","B","C")

Answer

new ArrayList<>(List.of("A","B","C"))

Answer

Collections.unmodifiableList(new ArrayList<>(List.of("A","B","C")))

Answer

None of the above

Question 12

Given: Map map = new HashMap<>(); map.put("x", 10); map.put("y", 20); map.computeIfAbsent("x", k -> 30); map.computeIfPresent("z", (k,v) -> 40); System.out.println(map); What is the output?

Accepted Answer

{x=10, y=20}. `computeIfAbsent` only inserts a mapping if the key is absent, and since "x" already exists with value 10, the lambda is not executed and the value remains 10. `computeIfPresent` only modifies a mapping if the key is present, and since "z" is not in the map, the lambda is not executed and no entry is added. Thus the map remains {x=10, y=20}.

Answer

Compilation fails

Answer

{x=30, y=20}

Answer

{x=30, y=20, z=40}

Answer

{x=10, y=20, z=40}

Question 13

Which of the following correctly creates a text block in Java?

Accepted Answer

"""line1
   line2""". It uses the Java text block syntax, which starts and ends with three double-quote characters (""") and places the content on a new line after the opening delimiter. The text block preserves the line break and indentation, making it ideal for multi-line strings without escape sequences.

Answer

"line1
line2"

Answer

'line1
line2'

Answer

"""line1
line2"""

Question 14

Refer to the exhibit. What is the output?

Accepted Answer

Count: 2. The stream filters out all elements equal to "A", leaving only elements that are not "A". Based on the list in the exhibit, there are exactly two such elements (e.g., "B" and "C"), so the count is 2.

Answer

Count: 3

Answer

Count: 1

Answer

Count: 4

Question 15

Which THREE statements are true about loops in Java?

Accepted Answer

The break statement can be used to exit a loop prematurely.. The break statement in Java is used to immediately terminate the execution of a loop (for, while, or do-while) and transfer control to the statement following the loop. This allows premature exit based on a condition, which is a fundamental control flow mechanism in Java.

Answer

A while loop always executes at least once.

Answer

A do-while loop may execute zero times if the condition is false.

Question 16

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 17

A team is developing a large enterprise application using Java 17. The application consists of multiple modules: core (provides logging and configuration), services (business logic), and web (REST endpoints). The modules are packaged as separate JAR files and deployed on a server. During runtime, the web module throws a java.lang.ClassNotFoundException for a class that is part of the core module. The core module's module-info.java exports the package containing the missing class. The web module's module-info.java requires core. However, the services module also needs the same class but uses a different version of it, causing conflicts. The team decides to use the class path for the conflicting package and the module path for the rest. They add the conflicting JAR to the class path and keep the other JARs on the module path. After this change, the web module still cannot find the class, but the services module works fine. What is the most likely cause of the issue?

Accepted Answer

The web module is a named module and cannot access classes from a split package that is also in the unnamed module.. When a named module (the web module) is on the module path, it cannot access classes from the unnamed module (the class path) if those classes belong to a package that is also exported by another named module on the module path. This creates a split package, which is forbidden by the Java module system. The core module exports the package, so the web module cannot load the class from the class path JAR, resulting in ClassNotFoundException.

Answer

The services module is using an automatic module, which automatically reads the unnamed module, while the web module is a named module that does not.

Answer

The class path is not scanned for JAR files unless the module path is empty.

Answer

The core module's module-info.java does not export the package to the web module; it only exports it to all modules.

Question 18

Which TWO of the following are valid ways to create a LocalDate object in Java 17?

Accepted Answer

LocalDate.of(2023, Month.JANUARY, 15). `LocalDate.of(int year, Month month, int dayOfMonth)` is a standard factory method that creates a `LocalDate` from explicit year, month, and day values. The `Month` enum provides type-safe month constants, making this a valid and commonly used approach.

Answer

LocalDate.from(Instant.now())

Answer

LocalDate.of(2023, 13, 1)

Answer

LocalDate.ofEpochDay("19375")

Question 19

A financial application deserializes objects received over the network using ObjectInputStream. To prevent deserialization attacks, which secure coding practice should be implemented?

Accepted Answer

Use an ObjectInputFilter to whitelist allowed classes.. ObjectInputFilter (introduced in Java 9) allows you to define a filter that whitelists only trusted classes during deserialization. By rejecting untrusted classes before they are deserialized, you prevent deserialization attacks such as remote code execution via gadget chains. This is the recommended secure coding practice per Oracle's secure coding guidelines for the Java I/O API.

Answer

Override readObject() in each serializable class to validate data.

Answer

Declare all fields as transient to prevent unwanted data exposure.

Answer

Encrypt the serialized data with AES before transmission.

Question 20

Which THREE are methods of the Map.Entry interface? (Java 17)

Accepted Answer

getValue(). The Map.Entry interface in Java defines the getValue() method, which returns the value associated with the entry's key. This method is part of the core contract for accessing key-value pairs within a Map.

Answer

getHash()

Answer

getValueOrDefault()