1Z0-829 Practice Test 4 — 25 Questions

Question 1

Which THREE of the following are valid ways to create a Stream<String>? (Choose three.)

Accepted Answer

Arrays.stream(new String[]{"a", "b"}). Option A is correct because Arrays.stream(T[] array) is a static factory method on java.util.Arrays that accepts an object array such as new String[]{"a", "b"} and returns a Stream whose elements are the array's elements. Option B is correct because Stream.of(T... values) is a static factory method on java.util.stream.Stream that takes a varargs of String values ("a", "b") and returns a Stream. Option C is correct because List.of("a", "b") creates an immutable List, and calling stream() on any Collection (including List) returns a Stream of its elements. Option D is not correct because "ab".chars() returns an IntStream of primitive int character values, not a Stream. Option E is not correct because Stream is an interface and cannot be instantiated with new Stream(); streams must be obtained via factory methods or from a source such as a collection or array.

Answer

"ab".chars()

Answer

new Stream<String>()

Question 2

A developer writes code to iterate over a list of strings and print each element. The code uses an enhanced for loop. Which statement is true about the enhanced for loop?

Accepted Answer

It can be used with arrays and any object that implements Iterable.. The enhanced for loop (for-each) in Java can iterate over arrays and any object that implements the Iterable interface, which includes all Collection classes (e.g., List, Set, Queue). This is because the for-each loop internally uses an iterator for Iterable objects or array indexing for arrays, making it a versatile construct for traversing elements without needing an explicit counter.

Answer

It can only be used with arrays.

Answer

It requires an explicit counter variable.

Answer

It allows removing elements from the collection during iteration without ConcurrentModificationException.

Question 3

You are responsible for a Java 17 application that processes user uploads. The application uses a custom AutoCloseable resource, UploadSession, which must always be closed after use to free server resources. A junior developer wrote the following code:

```
UploadSession session = new UploadSession();
try {
    session.upload(data);
    // more processing
} catch (UploadException e) {
    log.error("Upload failed", e);
} finally {
    session.close();
}
```

During a code review, you notice that the close() method of UploadSession throws a checked CloseException. The current code does not handle this exception. Which course of action should you recommend to ensure the application is robust and follows best practices?

Accepted Answer

Rewrite the code to use try-with-resources: try (UploadSession session = new UploadSession()) { ... } catch (UploadException e) { ... }. Try-with-resources automatically calls the close() method on the UploadSession resource when the try block exits, whether normally or abruptly. This eliminates the need for an explicit finally block and ensures that any checked exception thrown by close() is either caught or propagated according to the developer's declared exception handling, making the code both robust and concise.

Answer

Add a try-catch block inside the finally block to handle CloseException from session.close().

Answer

Declare the method with throws CloseException, and remove the finally block.

Answer

Keep the code as-is. The CloseException is not critical; it can be ignored.

Question 4

Which TWO statements about the java.util.Collections class are true?

Accepted Answer

Collections.synchronizedList(List) returns a synchronized list backed by the specified list.. Option D is correct because Collections.synchronizedList(List) returns a thread-safe wrapper around the given list, and the returned list is backed by the original list, so changes to one are reflected in the other. Option E is correct because Collections.unmodifiableList(List) returns an unmodifiable view of the specified list, meaning any attempt to modify it throws UnsupportedOperationException while reads pass through to the backing list. Options A, B, and C are incorrect because Collections.sort(List), Collections.reverse(List), and Collections.shuffle(List) all return void and mutate the list in place rather than returning a new list.

Answer

Collections.sort(List) returns a new sorted list.

Answer

Collections.reverse(List) returns a new reversed list.

Answer

Collections.shuffle(List) returns a new shuffled list.

Question 5

A method receives a List<String> and needs to transform it to a Map where the key is the first three characters of each string and the value is the string itself. If two strings have the same prefix, the later one should override the earlier. Which collector achieves this?

Accepted Answer

Collectors.toMap(s -> s.substring(0,3), Function.identity(), (a,b) -> b). `Collectors.toMap` with a merge function `(a, b) -> b` ensures that when duplicate keys (first three characters) occur, the later string in the stream order replaces the earlier one. The merge function is invoked on key collision, and returning `b` (the second argument) keeps the later value, satisfying the requirement.

Answer

Collectors.groupingBy(s -> s.substring(0,3))

Answer

Collectors.toMap(s -> s.substring(0,3), Function.identity())

Answer

Collectors.toConcurrentMap(s -> s.substring(0,3), Function.identity())

Question 6

A Java application uses a custom resource class implementing AutoCloseable. The close() method throws a checked exception. In a try-with-resources block, if both the try block and the close() method throw exceptions, which exception is propagated to the caller? Assume the resource is declared in try-with-resources.

Accepted Answer

The exception from the try block is the primary exception, and the close() exception is added as a suppressed exception.. In a try-with-resources block, when both the try block and the close() method throw exceptions, the exception from the try block is the primary exception propagated to the caller. The exception thrown by close() is added to the primary exception's suppressed exception list, as defined by the Java Language Specification (JLS §14.20.3.2). This ensures that the most relevant exception (the one from the application logic) is not masked by a resource-closing failure.

Answer

The exception from close() is always the primary exception.

Answer

Both exceptions are thrown simultaneously as a multi-catch exception.

Answer

The exception from the try block is always suppressed.

Question 7

A developer writes: List list = List.of(1, 2, 3); Optional opt = list.stream().reduce((a, b) -> a + b); System.out.println(opt.get()); What is the result?

Accepted Answer

6. The `reduce` method with a single argument (a `BinaryOperator`) returns an `Optional` because the stream might be empty. Here, the stream contains three integers, so the reduction computes `1 + 2 = 3`, then `3 + 3 = 6`, yielding `Optional[6]`. Calling `get()` on a non-empty `Optional` returns the contained value `6`, which is printed.

Answer

Optional[6]

Answer

Optional.empty

Answer

NoSuchElementException

Question 8

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 9

A method catches multiple exceptions using a multi-catch clause. Which statement about the exceptions in a multi-catch clause is correct?

Accepted Answer

The exceptions must be disjoint; if one is a subclass of another, the code will not compile.. Java requires that exception types in a multi-catch clause be disjoint (i.e., not in a subclass/superclass relationship). If one exception is a subclass of another, the code will not compile because the catch block would be unreachable for the subclass exception, violating the rule that catch blocks must be ordered from most specific to most general. This ensures that the multi-catch clause is unambiguous and that each exception type is distinct.

Answer

All exceptions in a multi-catch must be unchecked exceptions.

Answer

The multi-catch clause can have up to three exception types.

Answer

The exceptions can be in any order, and the first matching catch handles the exception.

Question 10

Given a try-with-resources statement where both the try block and the close method of the resource throw exceptions, which of the following is true about exception handling?

Accepted Answer

The try block exception is the primary exception; the close exception is suppressed.. In a try-with-resources statement, if both the try block and the resource's close() method throw exceptions, the exception from the try block is the primary exception, and any exception thrown by close() is added as a suppressed exception. This is defined by Java's try-with-resources semantics (JLS §14.20.3.2), ensuring the primary exception is not masked by resource cleanup failures.

Answer

The exception from the close method is the primary exception.

Answer

Both exceptions are thrown simultaneously, causing a multi-catch.

Answer

The close method exception is ignored if the try block succeeds.

Question 11

Which two statements about multi-catch blocks are correct?

Accepted Answer

A multi-catch block can be used with a finally block.. Option B is correct because a multi-catch block is simply an alternative form of a catch clause, so it can be freely combined with a finally block (and with other catch clauses) in the same try statement, e.g. try { ... } catch (IOException | SQLException e) { ... } finally { ... }. Option E is correct because the exception parameter types listed in a multi-catch must be disjoint — the compiler rejects alternatives where one type is a subclass of another (e.g. catch (IOException | FileNotFoundException e) fails), since the parameter is implicitly final and typed as the least upper bound of the alternatives. Option A is wrong because a multi-catch may combine checked and unchecked exception types, such as catch (IOException | IllegalArgumentException e), as long as the alternatives are disjoint. Option C is wrong because the multi-catch parameter is implicitly final, which is exactly why it cannot be reassigned inside the handler. Option D is wrong because multi-catch is independent of try-with-resources; it works with any try statement, with or without resources.

Answer

A multi-catch block cannot catch both checked and unchecked exceptions.

Answer

The variable in a multi-catch block is not implicitly final.

Answer

A multi-catch block can only be used with try-with-resources.

Question 12

To generate a cryptographically secure random number for a key generation algorithm, which class should be used?

Accepted Answer

SecureRandom. D is correct because `SecureRandom` is specifically designed to produce cryptographically strong random numbers suitable for key generation, using algorithms like SHA1PRNG or NativePRNG that meet FIPS 140-2 standards. Unlike other random number generators, it ensures unpredictability and resistance to reverse engineering, which is critical for security-sensitive operations.

Answer

ThreadLocalRandom

Answer

Math.random()

Answer

Random

Question 13

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

Accepted Answer

getValue(). The java.util.Map.Entry interface defines getKey() (option C), which returns the key corresponding to the entry, and getValue() (option A), which returns the value corresponding to the entry; both are core accessors used when iterating a map's entrySet(). It also defines setValue(V value) (option D), which replaces the value for this entry and returns the previous value, enabling in-place modification during iteration. Option B, getHash(), does not exist on Map.Entry (hashing is handled by hashCode() inherited from Object), and option E, getValueOrDefault(), is not a Map.Entry method — it is a default method on the Map interface (getOrDefault(Object key, V defaultValue)), so neither belongs here.

Answer

getHash()

Answer

getValueOrDefault()

Question 14

Which statement about Collection interface remove methods is correct?

Accepted Answer

Collection.remove(Object) removes the first occurrence and returns boolean.. The Collection interface's remove(Object) method removes the first occurrence of the specified element from the collection, if present, and returns true if the collection was modified (i.e., the element was found and removed). This behavior is defined in the Java Collections Framework and applies to all implementations of Collection, such as ArrayList and HashSet.

Answer

List.remove(int) removes element at index and returns the removed element.

Answer

Collection.remove(Object) removes all occurrences of the element.

Answer

Both B and C

Question 15

You are developing a Java application that processes sensitive user data. The application runs on a server with strict security policies. You need to read configuration properties from a file located at /etc/app/config.properties. The application uses a SecurityManager. During testing, you get a security exception: java.security.AccessControlException: access denied (java.io.FilePermission /etc/app/config.properties read). You have already added a file permission grant in the policy file for the application codebase. However, the exception persists. What is the most likely cause?

Accepted Answer

A library or caller on the execution stack does not have the required FilePermission.. Even if the application's own codebase has the required FilePermission, any library or caller on the execution stack that does not have the permission will cause an AccessControlException. The SecurityManager performs stack inspection: every class on the call stack must have the required permission. If a library or framework method invoked by your code lacks the grant, the check fails.

Answer

The application codebase URL in the policy file is incorrect.

Answer

The file path is relative and needs to be resolved against user.dir.

Answer

The policy file is not being loaded because the JVM was not started with -Djava.security.policy.

Question 16

You are developing an online bookstore application. You have a list of Book objects, each with fields: String title, double price, and String genre. You need to generate a report that lists the total price of books in each genre, but only for genres where the average price is greater than $20.00. You are using Java 17 and streams. Which approach correctly accomplishes this task?

Accepted Answer

books.stream()
    .collect(Collectors.groupingBy(Book::getGenre,
             Collectors.mapping(Book::getPrice, Collectors.toList())))
    .entrySet().stream()
    .filter(e -> e.getValue().stream().mapToDouble(Double::doubleValue).average().orElse(0) > 20)
    .collect(Collectors.toMap(Map.Entry::getKey,
             e -> e.getValue().stream().mapToDouble(Double::doubleValue).sum()));. It first groups books by genre, collecting prices into lists, then filters entries where the average price exceeds $20 using `mapToDouble` and `average()`, and finally sums the prices for those genres. This two-step process correctly computes the average per genre before filtering, then sums the total per genre.

Answer

books.stream()
    .filter(b -> b.getPrice() > 20)
    .collect(Collectors.groupingBy(Book::getGenre,
             Collectors.summingDouble(Book::getPrice)));

Answer

books.stream()
    .collect(Collectors.groupingBy(Book::getGenre,
             Collectors.averagingDouble(Book::getPrice)))
    .entrySet().stream()
    .filter(e -> e.getValue() > 20)
    .collect(Collectors.toMap(Map.Entry::getKey, e -> {
        return books.stream().filter(b -> b.getGenre().equals(e.getKey())).mapToDouble(Book::getPrice).sum();
    }));

Answer

books.stream()
    .collect(Collectors.groupingBy(Book::getGenre,
             Collectors.summingDouble(Book::getPrice)))
    .entrySet().stream()
    .filter(e -> e.getValue() > 20)
    .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));

Question 17

A developer wants to ensure that a block of code always executes regardless of whether an exception occurs or not, and that any exception thrown in the block is not swallowed. Which construct should be used?

Accepted Answer

try-finally. The try-finally construct ensures that the finally block always executes after the try block, regardless of whether an exception occurs, and it does not catch or swallow any exception. This meets the requirement of guaranteed execution without suppressing the exception, as the exception propagates up the call stack.

Answer

try-catch with empty catch block

Answer

try-catch-finally with catch that rethrows the exception

Answer

try-with-resources without catch

Question 18

Consider the following code snippet:

try {
    // some code
} catch (IOException e) {
    // handle
} catch (FileNotFoundException e) { // Line X
    // handle
}

What will be the result?

Accepted Answer

Compilation fails at Line X with an error about an exception already caught.. In Java, when catching exceptions, the more specific exception subclass must be caught before the more general superclass. FileNotFoundException is a subclass of IOException, so catching IOException first makes the catch for FileNotFoundException unreachable, causing a compilation error at Line X.

Answer

The code compiles and runs without issues.

Answer

The code compiles but throws a ClassCastException at runtime.

Answer

The code compiles but the second catch never executes.

Question 19

Given the exhibit showing output from a program that uses try-with-resources, which of the following best describes the program?

Accepted Answer

Both the try block and the close method threw exceptions.. The output shows both a primary exception from the try block and a suppressed exception from the close method. In try-with-resources, if both the try block and the close method throw exceptions, the primary exception from the try block is propagated, and the close method's exception is added as a suppressed exception. The output displays both exceptions, confirming that both occurred.

Answer

The try block threw an exception, but the resource closed successfully.

Answer

Only the close method threw an exception, and the try block did not throw.

Answer

The close method threw an exception, and the try block completed normally.

Question 20

What is the likely cause of this compilation error?
```java
String day = "Monday";
int dayNum = switch (day) {
    case 1 -> 1;
    case 2 -> 2;
    default -> 0;
};
System.out.println(dayNum);
```

Accepted Answer

The switch selector is a String but case labels are int constants.. In a Java switch expression, the selector type and case label types must be compatible. If the selector is a String, the case labels must be String constants; int constants would cause a compilation error due to type mismatch. Options A, B, and C describe syntax issues that are not the primary cause here.

Answer

The switch expression uses arrow syntax but the keys are not unique.

Answer

The switch expression is missing a default case.

Answer

The switch expression is not assigned to a variable.