1Z0-829 Practice Test 25 — 15 Questions

Question 1

Which two statements are true about Java module declarations? (Choose two.)

Accepted Answer

A qualified export allows access to the exported package only to specific modules.. A qualified export in a Java module declaration (using the 'exports ... to ...' syntax) restricts access to the exported package only to the specific modules listed after the 'to' keyword. This provides fine-grained control over which other modules can use the exported types, enhancing encapsulation and security.

Answer

The uses directive is used to specify that a module provides a service implementation.

Answer

A module can read another module only if it explicitly requires it.

Answer

The requires directive can be used to specify a module that is optional.

Question 2

A team is designing a logging framework. The framework's core method log(String message) may throw a checked LogException if the logging system fails. The team wants to allow callers to choose whether to handle the exception or declare it as thrown. Which declaration of the log method satisfies this requirement?

Accepted Answer

public void log(String message) throws LogException { ... }. It declares the checked exception LogException in the throws clause, which forces callers to either handle it with a try-catch or propagate it by declaring throws in their own method. This satisfies the requirement that callers can choose how to deal with the exception, as checked exceptions must be acknowledged at compile time.

Answer

public void log(String message) { ... }

Answer

public void log(String message) throws Error { ... }

Answer

public void log(String message) throws RuntimeException { ... }

Question 3

Consider: List<String> list = Arrays.asList("A", "B", "C"); list.add("D"); What is the result?

Accepted Answer

An UnsupportedOperationException is thrown. The `Arrays.asList()` method returns a fixed-size list backed by the specified array. This list does not support structural modification operations like `add()` or `remove()`. Calling `add()` on such a list throws an `UnsupportedOperationException` at runtime.

Answer

An ArrayIndexOutOfBoundsException is thrown

Answer

The list becomes [A, B, C, D]

Answer

A ClassCastException is thrown

Question 4

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 5

A class that stores sensitive user data implements Serializable. To minimize security exposure from deserialization attacks, which modification is the best practice?

Accepted Answer

Declare the sensitive fields as transient.. Declaring sensitive fields as transient prevents them from being serialized, so they are not written to the stream and cannot be deserialized. This directly eliminates the attack surface for deserialization exploits targeting those fields, as the default serialization mechanism skips transient fields entirely.

Answer

Override writeObject to manually exclude the sensitive fields.

Answer

Implement Externalizable and override readExternal and writeExternal.

Answer

Remove the implements Serializable clause from the class declaration.

Question 6

Given the exhibit, what is the output?

Accepted Answer

12.50%. (12.50%) because the code uses `NumberFormat.getPercentInstance()` which formats a decimal value as a percentage by multiplying it by 100 and appending a '%' sign. The input value 0.125 is formatted as '12.50%' with two decimal places by default.

Answer

0.125

Answer

%12.50

Answer

12.5%

Question 7

Which class is best suited for reading integer tokens from a string containing space-separated integers?

Accepted Answer

Scanner. Scanner is best suited because it provides built-in methods like nextInt() that can parse space-separated integer tokens directly from a string, handling whitespace delimiters automatically. It is designed for parsing formatted input, making it the ideal choice for this task.

Answer

InputStreamReader

Answer

BufferedReader

Answer

DataInputStream

Question 8

An organization has a monolithic Java application built with Java 8 and deployed on a traditional classpath. They are migrating to Java 17 and want to use the module system to improve encapsulation. They have a jar file 'legacy.jar' that contains packages under 'com.legacy' and does not have a module-info.class. Which approach should they take to allow other modules to depend on this jar?

Accepted Answer

Place the jar on the module path; it becomes an automatic module.. When a JAR file without a module-info.class is placed on the module path, Java treats it as an automatic module. This allows other modules to depend on it by name (derived from the JAR filename) and grants it access to all other modules, effectively bridging the gap between the classpath and the module system during migration.

Answer

Add a module-info.class file to the jar using jar tool.

Answer

Place the jar on the classpath; it becomes an unnamed module.

Answer

Use jmod tool to convert the jar into a JMOD file.

Question 9

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 10

Which TWO correctly describe the behavior of the following code?

```java
int x = 10;
switch (x) {
    case 10: System.out.print("ten ");
    default: System.out.print("default ");
    case 20: System.out.print("twenty ");
}
```

Accepted Answer

The output is 'ten default twenty '.. In a Java switch statement, once a matching case is found, all subsequent cases (including the default case) are executed in order until a break statement is encountered. Here, case 10 matches, so it prints 'ten ', then falls through to default (prints 'default '), then falls through to case 20 (prints 'twenty '), producing 'ten default twenty '. This is known as fall-through behavior.

Answer

The default case is never executed because a matching case exists.

Answer

The output is 'ten default ' because case 20 is skipped.

Answer

The code does not compile because default must be the last case.

Question 11

Which three are terminal operations of the Stream interface? (Choose three.)

Accepted Answer

reduce. (reduce) is correct because it is a terminal operation that processes all elements of a stream to produce a single result (e.g., sum, concatenation). Terminal operations trigger the stream pipeline execution and close the stream, after which no further operations can be performed.

Answer

filter

Answer

map

Question 12

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.

Question 13

Given: int a=5, b=10; String result = (a > b) ? "greater" : (a < b) ? "less" : "equal"; What is result?

Accepted Answer

"less". The ternary operator is right-associative, so the expression is parsed as `a > b ? "greater" : (a < b ? "less" : "equal")`. Since `a=5` and `b=10`, `a > b` is false, so the second operand of the outer ternary is evaluated: `a < b` is true, so the inner ternary returns `"less"`. The code compiles and runs without error, producing `"less"`.

Answer

"equal"

Answer

"greater"

Answer

Compilation error

Question 14

A developer writes the following code using Java 17: List list = new ArrayList<>(); list.add("A"); list.add("B"); list.add(10); What is the result?

Accepted Answer

Compilation error. The code attempts to add an integer (10) to a `List`, which is a compile-time type mismatch. Java's generics enforce type safety at compile time, so adding an `int` (autoboxed to `Integer`) to a `List` results in a compilation error. The code will not compile, and no runtime execution occurs.

Answer

The code compiles and runs successfully

Answer

ClassCastException at runtime

Answer

Compiler warning, but runs with unchecked operation

Question 15

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.