Oracle 1z0-830 : Java SE 21 Developer Professional

1z0-830 real exams

Exam Code: 1z0-830

Exam Name: Java SE 21 Developer Professional

Updated: Aug 23, 2026

Q & A: 85 Questions and Answers

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Oracle 1z0-830 Exam Syllabus Topics:

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

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


2. Given:
java
ExecutorService service = Executors.newFixedThreadPool(2);
Runnable task = () -> System.out.println("Task is complete");
service.submit(task);
service.shutdown();
service.submit(task);
What happens when executing the given code fragment?

A) It prints "Task is complete" twice, then exits normally.
B) It exits normally without printing anything to the console.
C) It prints "Task is complete" once and throws an exception.
D) It prints "Task is complete" once, then exits normally.
E) It prints "Task is complete" twice and throws an exception.


3. Given:
java
try (FileOutputStream fos = new FileOutputStream("t.tmp");
ObjectOutputStream oos = new ObjectOutputStream(fos)) {
fos.write("Today");
fos.writeObject("Today");
oos.write("Today");
oos.writeObject("Today");
} catch (Exception ex) {
// handle exception
}
Which statement compiles?

A) fos.writeObject("Today");
B) oos.write("Today");
C) oos.writeObject("Today");
D) fos.write("Today");


4. Which of the following doesnotexist?

A) BiSupplier<T, U, R>
B) BooleanSupplier
C) Supplier<T>
D) LongSupplier
E) They all exist.
F) DoubleSupplier


5. Given:
java
System.out.print(Boolean.logicalAnd(1 == 1, 2 < 1));
System.out.print(Boolean.logicalOr(1 == 1, 2 < 1));
System.out.print(Boolean.logicalXor(1 == 1, 2 < 1));
What is printed?

A) truefalsetrue
B) truetruetrue
C) Compilation fails
D) falsetruetrue
E) truetruefalse


Solutions:

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

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