Oracle 1z1-830 : Java SE 21 Developer Professional

Exam Code: 1z1-830

Exam Name: Java SE 21 Developer Professional

Updated: Oct 07, 2026

Q & A: 85 Questions and Answers

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Oracle 1z1-830 Exam Syllabus Topics:

Section	Weight	Objectives
Topic 1: Handling Date, Time, Text, Numeric and Boolean Values	12%	- Use primitives and wrapper classes, evaluate expressions and apply type conversions - Use Date-Time API: LocalDate, LocalTime, LocalDateTime, Period, Duration, Instant, ZonedDateTime - Manipulate text, text blocks, String, StringBuilder and StringBuffer
Topic 2: Concurrency and Multithreading	10%	- Synchronization, locks, concurrent collections, thread safety - Thread lifecycle, Runnable, Callable, ExecutorService, virtual threads
Topic 3: Java I/O and Localization	5%	- Resource bundles, locale, formatting messages, numbers, dates - File I/O, NIO.2, streams, readers/writers, serialization
Topic 4: Using Object-Oriented Concepts	20%	- Classes, records, objects, constructors, initializers, methods, fields, encapsulation - Inheritance, abstract classes, sealed classes, interfaces, polymorphism - Overloading, overriding, Object class methods, immutable objects - Enums, nested classes, local variable type inference
Topic 5: Working with Arrays and Collections	12%	- Collections Framework: List, Set, Map, Deque, Queue, sorting, searching - Declare, instantiate, initialize, use arrays and multidimensional arrays
Topic 6: Advanced Features and Annotations	3%	- Annotations, built-in annotations, custom annotations - Generics, type parameters, wildcards, type erasure
Topic 7: Functional Programming and Streams	15%	- Optional class, primitive streams - Lambda expressions, functional interfaces, method references - Stream API: create, intermediate/terminal operations, parallel streams, grouping, partitioning
Topic 8: Controlling Program Flow	10%	- Decision constructs: if-else, switch expressions and statements, pattern matching - Loops: for, enhanced for, while, do-while, break, continue, return
Topic 9: Modules and Packaging	5%	- Module system: module-info.java, exports, requires, provides, uses - Create and use JAR files, modular and non-modular builds
Topic 10: Handling Exceptions	8%	- Create and use custom exceptions, throw, throws - Exception hierarchy, try-catch-finally, multi-catch, try-with-resources

Oracle Java SE 21 Developer Professional Sample Questions:

Question #1

Which two of the following aren't the correct ways to create a Stream?

A. Stream stream = Stream.empty();
B. Stream stream = Stream.of();
C. Stream stream = Stream.ofNullable("a");
D. Stream stream = new Stream();
E. Stream stream = Stream.generate(() -> "a");
F. Stream<String> stream = Stream.builder().add("a").build();

Reveal Solution Discussion 0

Correct Answer: D,F 🗳️

Question #2

Given:
java
CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<>();
list.add("A");
list.add("B");
list.add("C");
// Writing in one thread
new Thread(() -> {
list.add("D");
System.out.println("Element added: D");
}).start();
// Reading in another thread
new Thread(() -> {
for (String element : list) {
System.out.println("Read element: " + element);
}
}).start();
What is printed?

A. It throws an exception.
B. It prints all elements, but changes made during iteration may not be visible.
C. It prints all elements, including changes made during iteration.
D. Compilation fails.

Reveal Solution Discussion 0

Correct Answer: B 🗳️

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Question #3

Given:
java
List<Long> 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. Compilation fails
B. Numbers from 1 to 25 randomly
C. An exception is thrown at runtime
D. Numbers from 1 to 1945 randomly
E. Numbers from 1 to 25 sequentially

Reveal Solution Discussion 0

Correct Answer: B 🗳️

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Question #4

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

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

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Correct Answer: C 🗳️

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Question #5

Given:
java
public class Versailles {
int mirrorsCount;
int gardensHectares;
void Versailles() { // n1
this.mirrorsCount = 17;
this.gardensHectares = 800;
System.out.println("Hall of Mirrors has " + mirrorsCount + " mirrors."); System.out.println("The gardens cover " + gardensHectares + " hectares.");
}
public static void main(String[] args) {
var castle = new Versailles(); // n2
}
}
What is printed?

A. Compilation fails at line n1.
B. Compilation fails at line n2.
C. nginx
Hall of Mirrors has 17 mirrors.
The gardens cover 800 hectares.
D. Nothing
E. An exception is thrown at runtime.

Reveal Solution Discussion 0

Correct Answer: A 🗳️

Explanation: Only visible for PassTorrent members. You can sign-up / login (it's free).

Oracle 1z1-830 : Java SE 21 Developer Professional

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