1Z0-829 Practice Test 19 — 15 Questions

Question 1

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 '.. Option D is correct because Java switch statements use fall-through: after case 10 matches and prints 'ten ', execution continues into the default label (printing 'default ') and then into case 20 (printing 'twenty '), yielding 'ten default twenty '. Option E is correct because the code compiles without error and runs, and the observed output is precisely the result of fall-through behavior rather than any break statements. Option A is wrong because default is not skipped when a matching case exists; without a break, control falls into default. Option B is wrong because case 20 is not skipped; fall-through reaches it and prints 'twenty '. Option C is wrong because Java does not require default to be the last case; default may appear anywhere in the switch.

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 2

A developer needs to iterate over a list of strings and print each string, but stop if the string equals "STOP". Which loop construct is most appropriate?

Accepted Answer

for (String s : list) { if (s.equals("STOP")) break; System.out.println(s); }. The enhanced for loop with a break statement is ideal for iterating over a collection and stopping when a condition is met. When the string "STOP" is encountered, break exits the loop immediately, ensuring no further strings are printed. This is simple, readable, and precisely matches the requirement to stop processing upon encountering "STOP".

Answer

for (String s : list) { if (s.equals("STOP")) continue; System.out.println(s); }

Answer

while (true) { for (String s : list) { if (s.equals("STOP")) break; System.out.println(s); } }

Answer

for (int i = 0; i < list.size(); i++) { if (list.get(i).equals("STOP")) return; System.out.println(list.get(i)); }

Question 3

A developer is implementing a method that reads a file and parses its contents. The method should ensure that any resources opened during the process are properly closed, even if an exception occurs. Which approach guarantees resource closure with minimal code?

Accepted Answer

Use try-with-resources with the resource declared in the try clause.. Try-with-resources automatically closes any resource that implements `AutoCloseable` (or `Closeable`) at the end of the try block, regardless of whether an exception occurs. This guarantees resource closure with minimal code, as the developer does not need to write explicit `close()` calls or manage finally blocks.

Answer

Use a try-catch block and close the resource inside the catch block.

Answer

Use a try block followed by a finally block without catch.

Answer

Use a try-catch-finally block and call close() in the finally block.

Question 4

Given: List words = Arrays.asList("apple", "banana", "cherry"); Map> map = words.stream().collect(Collectors.groupingBy(String::length)); System.out.println(map); What is the output?

Accepted Answer

{5=[apple], 6=[banana, cherry]}. The `groupingBy` collector groups stream elements by a classifier function, here `String::length`. Each distinct length becomes a key in the map, and the values are lists of strings with that length. "apple" (length 5) maps to key 5, "banana" and "cherry" (both length 6) map to key 6, producing `{5=[apple], 6=[banana, cherry]}`.

Answer

[apple, banana, cherry]

Answer

{5=[5], 6=[6, 6]}

Answer

{apple=[5], banana=[6], cherry=[6]}

Question 5

A HashMap uses a mutable object as a key. After adding the key-value pair, the key's fields are changed such that its hashCode changes. Which statement is true?

Accepted Answer

The value may not be retrievable using the modified key. When a HashMap uses a mutable object as a key and the key's hashCode changes after insertion, the key is stored in the bucket corresponding to its original hash code. The modified key's new hash code will likely map to a different bucket during retrieval, so the value may not be found. Option B is correct because the value may not be retrievable using the modified key, depending on whether the new hash code leads to the same bucket and whether equals() still matches.

Answer

The value can still be retrieved using the modified key

Answer

The entry is automatically moved to the correct bucket

Answer

An IllegalArgumentException is thrown when modifying the key

Question 6

Which TWO statements are true about the Java module system (JPMS) as of Java 17?

Accepted Answer

A named module is defined by a module-info.class file placed in the root of the module.. A named module in JPMS is defined by a module-info.class file (compiled from module-info.java) placed in the root directory of the module. This file declares the module's name, dependencies, and exported packages, making it a fundamental requirement for a named module.

Answer

An automatic module can contain a module-info.class file.

Answer

A jar file placed on the classpath that lacks module-info.class becomes an automatic module.

Answer

A named module can read an unnamed module by default.

Question 7

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

Accepted Answer

It is an unchecked exception.. 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 8

Arrange the steps to override equals() and hashCode() correctly in Java.

Accepted Answer

Override equals() with @Override, check identity (==), check null/class, cast, compare fields, override hashCode() with @Override, use Objects.hash() with same fields. equals() and hashCode() must be consistent: if two objects are equal, they must have the same hash code. Use Objects.hash() for hashCode().

Answer

Override hashCode() with @Override and Objects.hash(), then override equals() with @Override, check identity, cast, compare fields (skip type/null check)

Answer

Override equals() with @Override, check identity, cast directly compare fields, override hashCode() with @Override using random values

Answer

Override equals() with @Override, check identity, check type, override hashCode() with @Override and Objects.hash(), then cast and compare fields

Question 9

Match each Java collection class to its underlying data structure.

Accepted Answer

ArrayList: Resizable array. ArrayList uses a resizable array; LinkedList uses a doubly linked list; HashSet uses a hash table; TreeSet uses a red-black tree. Common confusions involve mixing up TreeMap with ArrayList or HashMap with TreeMap.

Answer

HashMap: Red-black tree

Answer

TreeMap: Resizable array

Question 10

Arrange the steps to use a lambda expression to sort a list of strings by length.

Accepted Answer

Start by creating a list of strings. Then write a lambda expression that uses Integer.compare to compare string lengths. Then pass the lambda to the Collections.sort method. Finally, print the sorted list.. Comparator is a functional interface; lambda provides concise implementation. Integer.compare() handles comparison safely.

Answer

Start by writing a lambda expression that uses Integer.compare to compare string lengths. Then create a list of strings. Then pass the lambda to the Collections.sort method. Finally, print the sorted list.

Answer

Start by creating a list of strings. Then pass the lambda to the Collections.sort method. Then write a lambda expression that uses Integer.compare to compare string lengths. Finally, print the sorted list.

Answer

Start by creating a list of strings. Then write a lambda expression that uses Integer.compare to compare string lengths. Then print the sorted list. Finally, pass the lambda to the Collections.sort method.

Question 11

Given: Set set = new HashSet<>(List.of(1,2,3)); List list = new ArrayList<>(set); Collections.sort(list); System.out.println(list); What is the output?

Accepted Answer

[1,2,3]. The code creates a HashSet from a List of 1, 2, 3, then copies it into an ArrayList. HashSet does not guarantee order, but Collections.sort() sorts the list in natural ascending order (1, 2, 3). The output is [1,2,3], making option C correct.

Answer

[3,2,1]

Answer

Compilation fails

Answer

[1,2]

Answer

[1,3,2]

Question 12

Which TWO approaches are recommended to secure Java I/O operations? (Choose two.)

Accepted Answer

Use try-with-resources to ensure proper resource closure.. Option A is correct because try-with-resources (introduced in Java 7) automatically invokes close() on any AutoCloseable resource such as InputStream, OutputStream, Reader, or Writer at the end of the try block, guaranteeing closure even if an exception is thrown and preventing resource leaks that could otherwise expose file handles or leave data unflushed. Option E is correct because path traversal attacks (e.g., "../" sequences) and injection of malicious filenames occur when untrusted input is concatenated directly into file paths; validating and sanitizing user input before constructing paths (or using canonical path checks) prevents unauthorized file access outside the intended directory. Option B is not a security measure — BufferedInputStream only improves I/O performance through buffering and does not address confidentiality, integrity, or access control. Option C is incorrect because implementing Serializable merely enables object serialization and actually introduces security risks such as deserialization vulnerabilities; it does not secure I/O operations. Option D is incorrect because FileLock only coordinates concurrent access among processes to prevent data corruption; it is not a recommended general security control and does not authenticate or authorize access.

Answer

Use BufferedInputStream to wrap FileInputStream for better performance.

Answer

Use Serializable interface for all data objects.

Answer

Use FileLock to prevent concurrent write access.

Question 13

Consider the following code:

public void process() throws Exception {
    try {
        riskyMethod();
    } catch (IOException | SQLException e) {
        throw e;
    }
}

Assuming riskyMethod() declares both IOException and SQLException, what is the result?

Accepted Answer

The code compiles and runs correctly.. In Java 7+, multi-catch variables are implicitly final, so they can be rethrown without a cast. The compiler knows that the thrown exception is exactly one of the caught types (IOException or SQLException), and since both are checked exceptions declared in the method signature, the code compiles and runs correctly. Option D is correct.

Answer

Compilation fails because you cannot rethrow a multi-catch variable.

Answer

Compilation fails because the catch variable must be cast to Exception.

Answer

The code compiles, but throws a ClassCastException at runtime.

Question 14

A method receives an InputStream and needs to compute its MD5 hash while reading the data. Which approach is most efficient?

Accepted Answer

Use DigestInputStream wrapping the original stream, then read the stream. `DigestInputStream` is a built-in Java class that computes a message digest (e.g., MD5) on the fly as data is read from the underlying stream. This avoids buffering the entire stream into memory, making it both memory-efficient and CPU-efficient for large or streaming data sources.

Answer

Read all bytes into a byte array, then compute hash using MessageDigest

Answer

Use a custom filter that hashes bytes during read

Answer

Use Scanner to read tokens and update hash

Question 15

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

Accepted Answer

Duration represents a time-based amount of time, such as hours, minutes, seconds.. The java.time.Duration class models a time-based amount of time in terms of seconds and nanoseconds, which can represent hours, minutes, seconds, and smaller units. It is designed for time-based quantities, not date-based ones like days, months, or years.

Answer

Duration.ofDays(1) returns a Duration that is daylight-saving-safe.

Answer

Duration.between(LocalDate.now(), LocalDate.now().plusDays(1)) returns a Duration of 1 day.

Answer

Duration can represent a period of months.