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Oracle 1z0-830 exam : Java SE 21 Developer Professional

1z0-830 Exam Questions
  • Exam Code: 1z0-830
  • Exam Name: Java SE 21 Developer Professional
  • Updated: Aug 05, 2026
  • Q & A: 85 Questions and Answers
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Oracle 1z0-830 Exam Syllabus Topics:

SectionWeightObjectives
Topic 1: Functional Programming and Streams15%- Stream API: create, intermediate/terminal operations, parallel streams, grouping, partitioning
- Lambda expressions, functional interfaces, method references
- Optional class, primitive streams
Topic 2: Handling Exceptions8%- Exception hierarchy, try-catch-finally, multi-catch, try-with-resources
- Create and use custom exceptions, throw, throws
Topic 3: Modules and Packaging5%- Create and use JAR files, modular and non-modular builds
- Module system: module-info.java, exports, requires, provides, uses
Topic 4: Using Object-Oriented Concepts20%- Enums, nested classes, local variable type inference
- Overloading, overriding, Object class methods, immutable objects
- Classes, records, objects, constructors, initializers, methods, fields, encapsulation
- Inheritance, abstract classes, sealed classes, interfaces, polymorphism
Topic 5: Handling Date, Time, Text, Numeric and Boolean Values12%- Use Date-Time API: LocalDate, LocalTime, LocalDateTime, Period, Duration, Instant, ZonedDateTime
- Manipulate text, text blocks, String, StringBuilder and StringBuffer
- Use primitives and wrapper classes, evaluate expressions and apply type conversions
Topic 6: Java I/O and Localization5%- File I/O, NIO.2, streams, readers/writers, serialization
- Resource bundles, locale, formatting messages, numbers, dates
Topic 7: Advanced Features and Annotations3%- Annotations, built-in annotations, custom annotations
- Generics, type parameters, wildcards, type erasure
Topic 8: Controlling Program Flow10%- Loops: for, enhanced for, while, do-while, break, continue, return
- Decision constructs: if-else, switch expressions and statements, pattern matching
Topic 9: Concurrency and Multithreading10%- Thread lifecycle, Runnable, Callable, ExecutorService, virtual threads
- Synchronization, locks, concurrent collections, thread safety
Topic 10: Working with Arrays and Collections12%- Collections Framework: List, Set, Map, Deque, Queue, sorting, searching
- Declare, instantiate, initialize, use arrays and multidimensional arrays

Oracle Java SE 21 Developer Professional Sample Questions:

1. Given:
java
sealed class Vehicle permits Car, Bike {
}
non-sealed class Car extends Vehicle {
}
final class Bike extends Vehicle {
}
public class SealedClassTest {
public static void main(String[] args) {
Class<?> vehicleClass = Vehicle.class;
Class<?> carClass = Car.class;
Class<?> bikeClass = Bike.class;
System.out.print("Is Vehicle sealed? " + vehicleClass.isSealed() +
"; Is Car sealed? " + carClass.isSealed() +
"; Is Bike sealed? " + bikeClass.isSealed());
}
}
What is printed?

A) Is Vehicle sealed? true; Is Car sealed? true; Is Bike sealed? true
B) Is Vehicle sealed? false; Is Car sealed? false; Is Bike sealed? false
C) Is Vehicle sealed? true; Is Car sealed? false; Is Bike sealed? false
D) Is Vehicle sealed? false; Is Car sealed? true; Is Bike sealed? true


2. Given:
java
Period p = Period.between(
LocalDate.of(2023, Month.MAY, 4),
LocalDate.of(2024, Month.MAY, 4));
System.out.println(p);
Duration d = Duration.between(
LocalDate.of(2023, Month.MAY, 4),
LocalDate.of(2024, Month.MAY, 4));
System.out.println(d);
What is the output?

A) UnsupportedTemporalTypeException
B) P1Y
UnsupportedTemporalTypeException
C) P1Y
PT8784H
D) PT8784H
P1Y


3. 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) 42 000,00 €
B) 42 k
C) 42000E
D) 42000


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


5. Given:
java
Object input = 42;
String result = switch (input) {
case String s -> "It's a string with value: " + s;
case Double d -> "It's a double with value: " + d;
case Integer i -> "It's an integer with value: " + i;
};
System.out.println(result);
What is printed?

A) It throws an exception at runtime.
B) It's a double with value: 42
C) It's a string with value: 42
D) It's an integer with value: 42
E) null
F) Compilation fails.


Solutions:

Question # 1
Answer: C
Question # 2
Answer: B
Question # 3
Answer: B
Question # 4
Answer: A
Question # 5
Answer: F

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