1Z0-829 Practice Test 1 — 10 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