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

  • Exam Code: 1z0-830
  • Exam Name: Java SE 21 Developer Professional
  • Updated: Oct 12, 2026
  • Q&As: 85 Questions and Answers

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Oracle 1z0-830 Exam Syllabus Topics:

SectionObjectives
Topic 1: Functional Programming- Use lambda expressions and method references
- Work with functional interfaces
- Process data using Stream API
Topic 2: Handling Date, Time, Text, Numeric and Boolean Values- Use String, StringBuilder, and related APIs
- Work with primitive wrappers and number formatting
- Use date, time, duration, period, and localization APIs
Topic 3: Controlling Program Flow- Apply decision statements and loops
- Work with records and sealed classes
- Use switch expressions and pattern matching
Topic 4: Exception Handling- Handle checked and unchecked exceptions
- Use try-with-resources
- Create custom exceptions
Topic 5: Java Concurrency- Work with concurrent collections and executors
- Use virtual threads
- Create and manage threads
Topic 6: Collections and Generics- Use List, Set, Map, Queue, and Deque implementations
- Apply generics and bounded types
- Use sequenced collections and maps
Topic 7: Java I/O and NIO- Read and write files
- Use Path, Files, and related APIs
- Process file system resources
Topic 8: Object-Oriented Programming- Implement encapsulation and abstraction
- Create and use classes, interfaces, enums, and records
- Apply inheritance and polymorphism
Topic 9: Annotations and JDBC- Use built-in and custom annotations
- Connect to databases using JDBC
- Execute SQL operations and process results
Topic 10: Modules and Packaging- Package and deploy applications
- Manage dependencies and exports
- Create and use Java modules

Oracle Java SE 21 Developer Professional Sample Questions:

Question #1

Given:
java
var now = LocalDate.now();
var format1 = new DateTimeFormatter(ISO_WEEK_DATE);
var format2 = DateTimeFormatter.ISO_WEEK_DATE;
var format3 = new DateFormat(WEEK_OF_YEAR_FIELD);
var format4 = DateFormat.getDateInstance(WEEK_OF_YEAR_FIELD);
System.out.println(now.format(REPLACE_HERE));
Which variable prints 2025-W01-2 (present-day is 12/31/2024)?

  • A. format3
  • B. format1
  • C. format2
  • D. format4
Reveal Solution  Discussion  0

Correct Answer: C  🗳️

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

Question #2

Given:
java
public class Test {
static int count;
synchronized Test() {
count++;
}
public static void main(String[] args) throws InterruptedException {
Runnable task = Test::new;
Thread t1 = new Thread(task);
Thread t2 = new Thread(task);
t1.start();
t2.start();
t1.join();
t2.join();
System.out.println(count);
}
}
What is the given program's output?

  • A. It's either 1 or 2
  • B. It's always 1
  • C. It's either 0 or 1
  • D. Compilation fails
  • E. It's always 2
Reveal Solution  Discussion  0

Correct Answer: D  🗳️

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

Question #3

Given:
java
int post = 5;
int pre = 5;
int postResult = post++ + 10;
int preResult = ++pre + 10;
System.out.println("postResult: " + postResult +
", preResult: " + preResult +
", Final value of post: " + post +
", Final value of pre: " + pre);
What is printed?

  • A. postResult: 15, preResult: 16, Final value of post: 6, Final value of pre: 6
  • B. postResult: 16, preResult: 15, Final value of post: 6, Final value of pre: 5
  • C. postResult: 15, preResult: 16, Final value of post: 5, Final value of pre: 6
  • D. postResult: 16, preResult: 16, Final value of post: 6, Final value of pre: 6
Reveal Solution  Discussion  0

Correct Answer: A  🗳️

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

Question #4

Which StringBuilder variable fails to compile?
java
public class StringBuilderInstantiations {
public static void main(String[] args) {
var stringBuilder1 = new StringBuilder();
var stringBuilder2 = new StringBuilder(10);
var stringBuilder3 = new StringBuilder("Java");
var stringBuilder4 = new StringBuilder(new char[]{'J', 'a', 'v', 'a'});
}
}

  • A. None of them
  • B. stringBuilder1
  • C. stringBuilder2
  • D. stringBuilder4
  • E. stringBuilder3
Reveal Solution  Discussion  0

Correct Answer: D  🗳️

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

Question #5

Given:
java
Optional o1 = Optional.empty();
Optional o2 = Optional.of(1);
Optional o3 = Stream.of(o1, o2)
.filter(Optional::isPresent)
.findAny()
.flatMap(o -> o);
System.out.println(o3.orElse(2));
What is the given code fragment's output?

  • A. Optional.empty
  • B. An exception is thrown
  • C. 2
  • D. 1
  • E. 0
  • F. Compilation fails
  • G. Optional[1]
Reveal Solution  Discussion  0

Correct Answer: D  🗳️

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

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