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Oracle Java SE 21 Developer Professional : 1z0-830
- Exam Code: 1z0-830
- Exam Name: Java SE 21 Developer Professional
- Updated: Oct 07, 2026
- Q & A: 85 Questions and Answers
About Oracle Java SE 21 Developer Professional : 1z0-830 Exam
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Oracle 1z0-830 Exam Syllabus Topics:
| Section | Weight | Objectives |
|---|---|---|
| Topic 1: Modules and Packaging | 5% | - Module system: module-info.java, exports, requires, provides, uses - Create and use JAR files, modular and non-modular builds |
| Topic 2: 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 3: Handling Date, Time, Text, Numeric and Boolean Values | 12% | - Use primitives and wrapper classes, evaluate expressions and apply type conversions - Manipulate text, text blocks, String, StringBuilder and StringBuffer - Use Date-Time API: LocalDate, LocalTime, LocalDateTime, Period, Duration, Instant, ZonedDateTime |
| Topic 4: Concurrency and Multithreading | 10% | - Thread lifecycle, Runnable, Callable, ExecutorService, virtual threads - Synchronization, locks, concurrent collections, thread safety |
| Topic 5: Advanced Features and Annotations | 3% | - Annotations, built-in annotations, custom annotations - Generics, type parameters, wildcards, type erasure |
| Topic 6: Functional Programming and Streams | 15% | - Lambda expressions, functional interfaces, method references - Stream API: create, intermediate/terminal operations, parallel streams, grouping, partitioning - Optional class, primitive streams |
| Topic 7: Handling Exceptions | 8% | - Exception hierarchy, try-catch-finally, multi-catch, try-with-resources - Create and use custom exceptions, throw, throws |
| Topic 8: Working with Arrays and Collections | 12% | - Collections Framework: List, Set, Map, Deque, Queue, sorting, searching - Declare, instantiate, initialize, use arrays and multidimensional arrays |
| Topic 9: Java I/O and Localization | 5% | - Resource bundles, locale, formatting messages, numbers, dates - File I/O, NIO.2, streams, readers/writers, serialization |
| Topic 10: Using Object-Oriented Concepts | 20% | - Classes, records, objects, constructors, initializers, methods, fields, encapsulation - Overloading, overriding, Object class methods, immutable objects - Enums, nested classes, local variable type inference - Inheritance, abstract classes, sealed classes, interfaces, polymorphism |
Oracle Java SE 21 Developer Professional Sample Questions:
Question #1
Given:
java
List<String> abc = List.of("a", "b", "c");
abc.stream()
.forEach(x -> {
x = x.toUpperCase();
});
abc.stream()
.forEach(System.out::print);
What is the output?
- A. An exception is thrown.
- B. ABC
- C. abc
- D. Compilation fails.
Correct Answer: C 🗳️
Explanation: Only visible for Free4Torrent members. You can sign-up / login (it's free).
Question #2
How would you create a ConcurrentHashMap configured to allow a maximum of 10 concurrent writer threads and an initial capacity of 42?
Which of the following options meets this requirement?
- A. var concurrentHashMap = new ConcurrentHashMap();
- B. var concurrentHashMap = new ConcurrentHashMap(42, 10);
- C. var concurrentHashMap = new ConcurrentHashMap(42);
- D. None of the suggestions.
- E. var concurrentHashMap = new ConcurrentHashMap(42, 0.88f, 10);
Correct Answer: E 🗳️
Explanation: Only visible for Free4Torrent members. You can sign-up / login (it's free).
Question #3
Given:
java
DoubleSummaryStatistics stats1 = new DoubleSummaryStatistics();
stats1.accept(4.5);
stats1.accept(6.0);
DoubleSummaryStatistics stats2 = new DoubleSummaryStatistics();
stats2.accept(3.0);
stats2.accept(8.5);
stats1.combine(stats2);
System.out.println("Sum: " + stats1.getSum() + ", Max: " + stats1.getMax() + ", Avg: " + stats1.getAverage()); What is printed?
- A. Sum: 22.0, Max: 8.5, Avg: 5.0
- B. An exception is thrown at runtime.
- C. Compilation fails.
- D. Sum: 22.0, Max: 8.5, Avg: 5.5
Correct Answer: D 🗳️
Explanation: Only visible for Free4Torrent members. You can sign-up / login (it's free).
Question #4
Given:
java
String textBlock = """
j \
a \t
v \s
a \
""";
System.out.println(textBlock.length());
What is the output?
- A. 10
- B. 11
- C. 12
- D. 14
Correct Answer: C 🗳️
Explanation: Only visible for Free4Torrent members. You can sign-up / login (it's free).
Question #5
Which of the following statements oflocal variables declared with varareinvalid?(Choose 4)
- A. var e;
- B. var b = 2, c = 3.0;
- C. var h = (g = 7);
- D. var a = 1;(Valid: var correctly infers int)
- E. var d[] = new int[4];
- F. var f = { 6 };
Correct Answer: A,B,E,F 🗳️
Explanation: Only visible for Free4Torrent members. You can sign-up / login (it's free).
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