Oracle 1Z0-830 Online Practice Questions and Exam Preparation

Oracle 1Z0-830 Online Questions & Answers

• Question 71:

  Which statement about sealed interfaces and records is correct?

  A. A record can never implement a sealed interface.
  B. A record must explicitly be listed in the permits clause to implement a sealed interface.
  C. A record implements sealed interfaces implicitly without permits.
  D. Sealed interfaces cannot be extended by records.
  B. A record must explicitly be listed in the permits clause to implement a sealed interface.

  ---

  Explanation

  When an interface is sealed, any implementing class or record must appear in its permits clause unless the interface and the record are in the same compilation unit.

• Question 72:

  Given:

  java

  var hauteCouture = new String[]{ "Chanel", "Dior", "Louis Vuitton" };

  var i = 0;

  do {

  System.out.print(hauteCouture[i] + " ");

  } while (i++ > 0);

  What is printed?

  A. Chanel
  B. Chanel Dior Louis Vuitton
  C. An ArrayIndexOutOfBoundsException is thrown at runtime.
  D. Compilation fails.
  A. Chanel

  ---

  Explanation

  Understanding the do-while Loop

  The do-while loop executes at least once before checking the condition.

  The condition i++ > 0 increments i after checking.

  Step-by-Step Execution

  Iteration 1:

  i = 0

  Prints: "Chanel"

  i++ updates i to 1

  Condition 1 > 0 is true , so the loop exits.

  Why Doesn't the Loop Continue?

  Since i starts at 0, the condition i++ > 0 is false after the first iteration .

  The loop exits immediately after printing "Chanel" .

  Final Output

  nginx

  Chanel

  Thus, the correct answer is:Chanel

  References: Java SE 21 - do-while Loop Java SE 21 - Post-Increment Behavior

• Question 73:

  Which of the following statements is correct about a final class?

  A. The final keyword in its declaration must go right before the class keyword.
  B. It must contain at least a final method.
  C. It cannot be extended by any other class.
  D. It cannot implement any interface.
  E. It cannot extend another class.
  C. It cannot be extended by any other class.

  ---

  Explanation

  In Java, the final keyword can be applied to classes, methods, and variables to impose certain restrictions.

  Final Classes:

  Definition:A class declared with the final keyword is known as a final class.

  Purpose:Declaring a class as final prevents it from being subclassed. This is useful when you want to ensure that the class's implementation remains unchanged and cannot be extended or modified through inheritance.

  Option Evaluations:

  A. The final keyword in its declaration must go right before the class keyword.

  This is correct. The syntax for declaring a final class is:

  java

  public final class ClassName {

  // class body

  }

  However, this statement is about syntax rather than the core characteristic of a final class.

  B. It must contain at least a final method.

  Incorrect. A final class can have zero or more methods, and none of them are required to be declared as final. The final keyword at the class level prevents inheritance, regardless of the methods' finality.

  C. It cannot be extended by any other class.

  Correct. The primary characteristic of a final class is that it cannot be subclassed. Attempting to do so will result in a compilation error.

  D. It cannot implement any interface.

  Incorrect. A final class can implement interfaces. Declaring a class as final restricts inheritance but does not prevent the class from implementing interfaces.

  E. It cannot extend another class.

  Incorrect. A final class can extend another class. The final keyword prevents the class from being subclassed but does not prevent it from being a subclass itself.

  Therefore, the correct statement about a final class is option C: "It cannot be extended by any other class."

• Question 74:

  Given:

  java

  Deque deque = new ArrayDeque<>();

  deque.offer(1);

  deque.offer(2);

  var i1 = deque.peek();

  var i2 = deque.poll();

  var i3 = deque.peek();

  System.out.println(i1 + " " + i2 + " " + i3);

  What is the output of the given code fragment?

  A. 1 2 1
  B. An exception is thrown.
  C. 2 2 1
  D. 2 1 2
  E. 1 2 2
  F. 1 1 2
  G. 2 1 1
  H. 1 1 1
  I. 2 2 2
  E. 1 2 2

  ---

  Explanation

  In this code, an ArrayDeque named deque is created, and the integers 1 and 2 are added to it using the offer method. The offer method inserts the specified element at the end of the deque.

  State of deque after offers:[1, 2]

  The peek method retrieves, but does not remove, the head of the deque, returning 1. Therefore, i1 is assigned the value 1. State of deque after peek:[1, 2]

  Value of i1:1

  The poll method retrieves and removes the head of the deque, returning 1. Therefore, i2 is assigned the value 1. State of deque after poll:[2]

  Value of i2:1

  Another peek operation retrieves the current head of the deque, which is now 2, without removing it.

  Therefore, i3 is assigned the value 2.

  State of deque after second peek:[2]

  Value of i3:2

  The System.out.println statement then outputs the values of i1, i2, and i3, resulting in 1 1 2.

• Question 75:

  Given:

  java

  double amount = 42_000.00;

  NumberFormat format = NumberFormat.getCompactNumberInstance(Locale.FRANCE, NumberFormat.Style.

  SHORT); System.out.println(format.format(amount)); What is the output?

  A. 42000E
  B. 42 000,00
  C. 42000
  D. 42 k
  D. 42 k

  ---

  Explanation

  In this code, a double variable amount is initialized to 42,000.00. The NumberFormat. getCompactNumberInstance(Locale.FRANCE, NumberFormat.Style.SHORT) method is used to obtain a compact number formatter for the French locale with the short style. The format method is then called to format the amount.

  The compact number formatting is designed to represent numbers in a shorter form, based on the patterns provided for a given locale. In the French locale, the short style represents thousands with a lowercase 'k'. Therefore, 42,000 is formatted as 42 k.

  Option Evaluations:

  A. 42000E: This format is not standard in the French locale for compact number formatting.

  B. 42 000,00 : This represents the number as a currency with two decimal places, which is not the compact form.

  C. 42000: This is the plain number without any formatting, which does not match the compact number format.

  D. 42 k: This is the correct compact representation of 42,000 in the French locale with the short style. Thus, option D (42 k) is the correct output.

• Question 76:

  Given:

  java

  var counter = 0;

  do {

  System.out.print(counter + " ");

  } while (++counter < 3);

  What is printed?

  A. 0 1 2 3
  B. 0 1 2
  C. 1 2 3 4
  D. 1 2 3
  E. An exception is thrown.
  F. Compilation fails.
  B. 0 1 2

  ---

  Explanation

  Understanding do-while Execution

  A do-while loop executes at least once before checking the condition.

  ++counter < 3 increments counter before evaluating the condition.

  Step-by-Step Execution

  Iteration 1:counter = 0, print "0", then ++counter becomes 1, condition 1 < 3 is true .

  Iteration 2:counter = 1, print "1", then ++counter becomes 2, condition 2 < 3 is true .

  Iteration 3:counter = 2, print "2", then ++counter becomes 3, condition 3 < 3 is false , so loop exits.

  Final Output

  0 1 2

  Thus, the correct answer is:0 1 2

  References:

  Java SE 21 - Control Flow Statements

  Java SE 21 - do-while Loop

• Question 77:

  Given:

  java

  List l1 = new ArrayList<>(List.of("a", "b"));

  List l2 = new ArrayList<>(Collections.singletonList("c"));

  Collections.copy(l1, l2);

  l2.set(0, "d");

  System.out.println(l1);

  What is the output of the given code fragment?

  A. [a, b]
  B. [d, b]
  C. [c, b]
  D. An UnsupportedOperationException is thrown
  E. An IndexOutOfBoundsException is thrown
  F. [d]
  C. [c, b]

  ---

  Explanation

  In this code, two lists l1 and l2 are created and initialized as follows:

  l1 Initialization:

  Created using List.of("a", "b"), which returns an immutable list containing the elements "a" and "b".

  Wrapped with new ArrayList<>(...) to create a mutable ArrayList containing the same elements.

  l2 Initialization:

  Created using Collections.singletonList("c"), which returns an immutable list containing the single element "c".

  Wrapped with new ArrayList<>(...) to create a mutable ArrayList containing the same element.

  State of Lists Before Collections.copy:

  l1: ["a", "b"]

  l2: ["c"]

  Collections.copy(l1, l2):

  The Collections.copy method copies elements from the source list (l2) into the destination list (l1). The destination list must have at least as many elements as the source list; otherwise, an IndexOutOfBoundsException is thrown.

  In this case, l1 has two elements, and l2 has one element, so the copy operation is valid. After copying, the first element of l1 is replaced with the first element of l2:

  l1 after copy: ["c", "b"]

  l2.set(0, "d"):

  This line sets the first element of l2 to "d".

  l2 after set: ["d"]

  Final State of Lists:

  l1: ["c", "b"]

  l2: ["d"]

  The System.out.println(l1); statement outputs the current state of l1, which is ["c", "b"]. Therefore, the correct answer is C: [c, b].

• Question 78:

  Which of the following can be the body of a lambda expression?

  A. Two statements
  B. An expression and a statement
  C. A statement block
  D. None of the above
  E. Two expressions
  C. A statement block

  ---

  Explanation

  In Java, a lambda expression can have two forms for its body:

  Single Expression:A concise form where the body consists of a single expression. The result of this expression is implicitly returned.

  Example:

  java

  (a, b) -> a + b

  In this example, (a, b) are the parameters, and a + b is the single expression that adds them together.

  Statement Block:A more detailed form where the body consists of a block of statements enclosed in braces {}. Within this block, you can have multiple statements, and if a return value is expected, you must explicitly use the return statement.

  Example:

  java

  (a, b) -> {

  int sum = a + b;

  System.out.println("Sum is: " + sum);

  return sum;

  }

  In this example, the lambda body is a statement block that performs multiple actions: it calculates the sum, prints it, and then returns the sum.

  Given the options:

  A. Two statements:While a lambda body can contain multiple statements, they must be enclosed within a statement block {}. Simply having two statements without braces is not valid syntax for a lambda expression.

  B. An expression and a statement:Similar to option A, if a lambda body contains more than one element (be it expressions or statements), they need to be enclosed in a statement block.

  C. A statement block:This is correct. A lambda expression can have a body that is a statement block, allowing multiple statements enclosed in braces.

  D. None of the above:This is incorrect since option C is valid.

  E. Two expressions:As with options A and B, multiple expressions must be enclosed in a statement block to form a valid lambda body. Therefore, the correct answer is C: A statement block.

• Question 79:

  Given:

  java

  public class ExceptionPropagation {

  public static void main(String[] args) {

  try {

  thrower();

  } catch (Exception e) {

  System.out.print("Chablis, ");

  } finally {

  }

  }

  static int thrower() {

  try {

  int i = 0;

  return i / i;

  } catch (NumberFormatException e) {

  return -1;

  } finally {

  System.out.print("Beaujolais Nouveau, ");

  }

  }

  }

  What is printed?

  A. Saint-Emilion
  B. Beaujolais Nouveau, Chablis, Saint-Emilion
  C. Beaujolais Nouveau, Chablis, Dom P
  D. Rose
  B. Beaujolais Nouveau, Chablis, Saint-Emilion

  ---

  Explanation

  Analyzing the thrower() Method Execution

  java

  int i = 0;

  return i / i;

  i / i evaluates to 0 / 0, which throws ArithmeticException (/ by zero) .

  Since catch (NumberFormatException e) does not match ArithmeticException, it is skipped.

  The finally block always executes, printing:

  nginx

  Beaujolais Nouveau,

  The exception propagates back to main().

  Handling the Exception in main()

  java

  try {

  thrower();

  } catch (Exception e) {

  System.out.print("Chablis, ");

  } finally {

  }

  Since thrower() throws ArithmeticException, it is caught by catch (Exception e).

  "Chablis, "is printed.

  Final Output

  nginx

  References:

  Java SE 21 - Exception Handling

  Java SE 21 - finally Block Execution

• Question 80:

  Given:

  java

  List cannesFestivalfeatureFilms = LongStream.range(1, 1945)

  .boxed()

  .toList();

  try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {

  cannesFestivalfeatureFilms.stream()

  .limit(25)

  .forEach(film -> executor.submit(() -> {

  System.out.println(film);

  }));

  }

  What is printed?

  A. Numbers from 1 to 25 sequentially
  B. Numbers from 1 to 25 randomly
  C. Numbers from 1 to 1945 randomly
  D. An exception is thrown at runtime
  E. Compilation fails
  B. Numbers from 1 to 25 randomly

  ---

  Explanation

  Understanding LongStream.range(1, 1945).boxed().toList();

  LongStream.range(1, 1945) generates a stream of numbers from 1 to 1944 .

  .boxed() converts the primitive long values to Long objects.

  .toList() (introduced in Java 16) creates an immutable list .

  Understanding Executors.newVirtualThreadPerTaskExecutor()

  Java 21 introduced virtual threads to improve concurrency.

  Executors.newVirtualThreadPerTaskExecutor()creates a new virtual thread per submitted task , allowing highly concurrent execution.

  Execution Behavior

  cannesFestivalfeatureFilms.stream().limit(25) # Limits the stream to the first 25 numbers (1 to 25).

  .forEach(film -> executor.submit(() -> System.out.println(film)))

  Each film is printed inside a virtual thread.

  Virtual threads execute asynchronously, meaning numbers arenot guaranteed to print sequentially .

  Output will contain numbers from 1 to 25, but their order is random due to concurrent execution.

  Possible Output (Random Order)

  python-repl

  The order may differ in each run due to concurrent execution.

  Thus, the correct answer is:"Numbers from 1 to 25 randomly."

  References:

  Java SE 21 - Virtual Threads

  Java SE 21 - Executors.newVirtualThreadPerTaskExecutor()