1Z0-829 Practice Test 21 — 15 Questions

Question 1

Given the code in the exhibit, which of the following is true about this custom exception?

Accepted Answer

It is an unchecked exception.. Option B is correct because the custom exception extends RuntimeException, which makes it an unchecked exception. Unchecked exceptions do not require handling or declaration in the method signature, and they can be used in multi-catch blocks.

Answer

It cannot be used with multi-catch because it is unchecked.

Answer

It must be caught or declared in the method signature.

Answer

It must implement the Serializable interface.

Question 2

Which THREE practices are recommended for effective exception handling? (Choose three.)

Accepted Answer

Throw exceptions early, catch them late, but handle them at the appropriate level.. Option A is correct because effective exception handling in Java recommends throwing exceptions as soon as an error is detected (fail-fast), catching them at a level where the error can be meaningfully handled (not too early), and handling them at the appropriate layer of abstraction. This prevents swallowing exceptions or losing context, and aligns with the principle of separation of concerns.

Answer

Define custom exceptions without providing any additional context.

Answer

Catch exceptions at the highest level of the application and log them generically.

Question 3

Refer to the exhibit. What is the purpose of this code?

Accepted Answer

Encrypt data.txt and write to data.enc. The code uses a CipherOutputStream with a cipher initialized in ENCRYPT_MODE, reading from data.txt and writing to data.enc, thus encrypting the plaintext file and producing an encrypted output file. This is the standard pattern for file encryption in Java using the JCA (Java Cryptography Architecture).

Answer

Compress data.txt and write to data.enc

Answer

Encrypt data.enc and write to data.txt

Answer

Decrypt data.txt and write to data.enc

Question 4

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. Option B is correct because 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 5

Given the exhibit, which statement about calling this function in a SELECT statement is true?

Accepted Answer

It can be called as `SELECT get_emp_name(101) FROM dual;`. Option C is correct because a function that does not modify database state (i.e., is not a transactional or DML operation) and returns a value can be invoked directly in a SQL SELECT statement. The function `get_emp_name` appears to be a stored function that returns an employee name based on an ID, and calling it as `SELECT get_emp_name(101) FROM dual;` is valid in Oracle SQL, provided the function is defined with sufficient purity levels (e.g., WNDS, WNPS) to be used in SQL context.

Answer

It must be called using the `CALL` statement.

Answer

It can only be called from a PL/SQL block, not from SQL.

Answer

It cannot be used in a SELECT because it contains a SELECT statement.

Question 6

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.. Option B is correct because 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 7

Refer to the exhibit. Which statement is true about the com.example.app.internal package?

Accepted Answer

It is accessible for deep reflection only by com.example.lib.. Option A is correct because the exhibit shows that `com.example.app.internal` is declared with `opens com.example.app.internal to com.example.lib`. The `opens` directive grants deep reflection (access to private members) at runtime, but only to the specified module `com.example.lib`. Other modules cannot reflectively access this package unless they are explicitly listed.

Answer

It is accessible for deep reflection by any module.

Answer

It is not accessible for reflection at all.

Answer

It is exported to all modules.

Question 8

Which of the following correctly uses a switch expression with multiple constants per case?

```java
int day = 2;
String result = switch (day) {
    case 1, 2, 3 -> "Weekday";
    case 6, 7 -> "Weekend";
    default -> "Invalid";
};
```

What is the value of result?

Accepted Answer

Weekday. The switch expression correctly uses multiple constants per case with the arrow syntax. Since day is 2, it matches case 1, 2, 3, so the expression evaluates to "Weekday". The switch expression is exhaustive (covers all possible int values via the default branch), so it compiles and runs without error.

Answer

The code does not compile because multiple constants are not allowed.

Answer

Invalid

Answer

Weekend

Question 9

A team is migrating a large legacy application from Java 8 to Java 17. The application consists of multiple JAR files that are placed on the classpath. Some of these JAR files have been updated to include module-info.class files, making them named modules. After migration, the application throws `IllegalAccessError` for several deep reflection calls that used to work in Java 8. The team has added `--add-opens` JVM flags to open the required packages, but the error persists. The application also uses a third-party library that is not modularized and is placed on the classpath. The team notices that the `--add-opens` flags are being ignored for packages in the modularized JARs. What is the most likely reason?

Accepted Answer

The modularized JARs are being loaded from the classpath, so they become unnamed modules, and `--add-opens` does not apply to unnamed modules.. Option C is correct because when a JAR file containing a module-info.class is placed on the classpath instead of the module path, it is treated as an unnamed module. The `--add-opens` JVM flag only applies to named modules (those on the module path) and has no effect on unnamed modules. Since the modularized JARs are loaded from the classpath, they become unnamed modules, and the `--add-opens` flags are ignored, causing the `IllegalAccessError` to persist.

Answer

The `--add-opens` flags are being overridden by other JVM flags.

Answer

The application does not have a module-info.java file for its own code.

Answer

The classpath is deprecated and ignored in Java 17, so all JARs are treated as modules.

Question 10

Which THREE of the following variable declarations are valid in Java 17?

Accepted Answer

List list = new ArrayList();. Option A is correct because `List` is a wildcard type that can hold any type, and `new ArrayList()` creates an `ArrayList` of a specific type (`String`). The wildcard `?` acts as a type-safe placeholder, allowing the assignment of a concrete parameterized type to an unbounded wildcard reference. This is valid because the wildcard represents an unknown type, and the list is read-only in terms of type safety (you cannot add elements except `null`).

Answer

List<Object> list = new ArrayList<String>();

Answer

List list = new ArrayList();

Question 11

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}. Option E is correct because `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 12

A developer needs to sort a List of Employee objects by salary (double) in descending order. Which approach is correct and efficient?

Accepted Answer

Collections.sort(list, (e1, e2) -> Double.compare(e2.getSalary(), e1.getSalary()));. Option C is correct because it uses `Collections.sort()` with a custom `Comparator` that performs an in-place sort of the original list, which is both efficient (no new list created) and correctly orders by salary descending via `Double.compare(e2.getSalary(), e1.getSalary())`. This avoids the overhead of stream pipeline creation and collection, and directly mutates the list as required.

Answer

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

Answer

list.stream().sorted((e1, e2) -> Double.compare(e2.getSalary(), e1.getSalary())).collect(Collectors.toList());

Answer

Collections.sort(list);

Question 13

Which statement about TreeSet is true when using a custom Comparator that does not define equals() consistently with compare()?

Accepted Answer

TreeSet considers two elements equal if the comparator returns 0.. TreeSet uses the compare() method of the provided Comparator (or the natural ordering's compareTo()) to determine element equality. When a custom Comparator returns 0 for two elements, TreeSet treats them as duplicates and does not add the second element, regardless of what equals() returns. This is specified in the Java Collections Framework documentation and is critical for maintaining the Set contract.

Answer

TreeSet uses equals() to determine duplicates.

Answer

TreeSet uses hashCode() for ordering.

Answer

TreeSet throws IllegalArgumentException if equals() is inconsistent.

Question 14

What is the result of the following code?
List<String> list = List.of("A", "B");
list.add("C");
System.out.println(list);

Accepted Answer

An exception is thrown at runtime. The `List.of()` factory method returns an immutable list. Calling `add()` on an immutable list throws an `UnsupportedOperationException` at runtime, so the code does not compile or run successfully. Option C is correct because the exception is thrown when the `add` method is invoked.

Answer

[A, B, C]

Answer

[A, B]

Answer

Compilation error

Question 15

When should LinkedList be preferred over ArrayList?

Accepted Answer

Frequent insertions and deletions at arbitrary positions. LinkedList is preferred over ArrayList when frequent insertions and deletions occur at arbitrary positions because LinkedList uses a doubly-linked list structure, allowing O(1) time for insertions/deletions once the node is located, whereas ArrayList requires shifting elements (O(n)) due to its underlying array. This makes D correct for scenarios with heavy modification in the middle of the list.

Answer

Frequent random access by index

Answer

Fast iteration over all elements

Answer

Minimal memory overhead

1Z0-829 Practice Test 21 — 15 Questions

Exhibit

1Z0-829 Practice Test 21 — 15 Questions

Exhibit