Oracle Java SE 21 Developer Professional : 1z1-830

1z1-830 real exams

Exam Code: 1z1-830

Exam Name: Java SE 21 Developer Professional

Updated: Aug 24, 2026

Q & A: 85 Questions and Answers

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Oracle 1z1-830 Exam Syllabus Topics:

SectionWeightObjectives
Advanced Features and Annotations3%- Generics, type parameters, wildcards, type erasure
- Annotations, built-in annotations, custom annotations
Concurrency and Multithreading10%- Synchronization, locks, concurrent collections, thread safety
- Thread lifecycle, Runnable, Callable, ExecutorService, virtual threads
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
Working with Arrays and Collections12%- Declare, instantiate, initialize, use arrays and multidimensional arrays
- Collections Framework: List, Set, Map, Deque, Queue, sorting, searching
Modules and Packaging5%- Module system: module-info.java, exports, requires, provides, uses
- Create and use JAR files, modular and non-modular builds
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
Controlling Program Flow10%- Loops: for, enhanced for, while, do-while, break, continue, return
- Decision constructs: if-else, switch expressions and statements, pattern matching
Handling Exceptions8%- Exception hierarchy, try-catch-finally, multi-catch, try-with-resources
- Create and use custom exceptions, throw, throws
Functional Programming and Streams15%- Stream API: create, intermediate/terminal operations, parallel streams, grouping, partitioning
- Lambda expressions, functional interfaces, method references
- Optional class, primitive streams
Java I/O and Localization5%- File I/O, NIO.2, streams, readers/writers, serialization
- Resource bundles, locale, formatting messages, numbers, dates

Oracle Java SE 21 Developer Professional Sample Questions:

1. Given:
java
final Stream<String> strings =
Files.readAllLines(Paths.get("orders.csv"));
strings.skip(1)
.limit(2)
.forEach(System.out::println);
And that the orders.csv file contains:
mathematica
OrderID,Customer,Product,Quantity,Price
1,Kylian Mbappe,Keyboard,2,25.50
2,Teddy Riner,Mouse,1,15.99
3,Sebastien Loeb,Monitor,1,199.99
4,Antoine Griezmann,Headset,3,45.00
What is printed?

A) An exception is thrown at runtime.
B) arduino
1,Kylian Mbappe,Keyboard,2,25.50
2,Teddy Riner,Mouse,1,15.99
3,Sebastien Loeb,Monitor,1,199.99
4,Antoine Griezmann,Headset,3,45.00
C) arduino
1,Kylian Mbappe,Keyboard,2,25.50
2,Teddy Riner,Mouse,1,15.99
D) arduino
2,Teddy Riner,Mouse,1,15.99
3,Sebastien Loeb,Monitor,1,199.99
E) Compilation fails.


2. Given:
java
Optional<String> optionalName = Optional.ofNullable(null);
String bread = optionalName.orElse("Baguette");
System.out.print("bread:" + bread);
String dish = optionalName.orElseGet(() -> "Frog legs");
System.out.print(", dish:" + dish);
try {
String cheese = optionalName.orElseThrow(() -> new Exception());
System.out.println(", cheese:" + cheese);
} catch (Exception exc) {
System.out.println(", no cheese.");
}
What is printed?

A) bread:Baguette, dish:Frog legs, cheese.
B) bread:bread, dish:dish, cheese.
C) bread:Baguette, dish:Frog legs, no cheese.
D) Compilation fails.


3. Given:
java
interface A {
default void ma() {
}
}
interface B extends A {
static void mb() {
}
}
interface C extends B {
void ma();
void mc();
}
interface D extends C {
void md();
}
interface E extends D {
default void ma() {
}
default void mb() {
}
default void mc() {
}
}
Which interface can be the target of a lambda expression?

A) None of the above
B) A
C) B
D) D
E) E
F) C


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) stringBuilder3
B) None of them
C) stringBuilder2
D) stringBuilder1
E) stringBuilder4


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) Compilation fails
C) truetruetrue
D) truetruefalse
E) falsetruetrue


Solutions:

Question # 1
Answer: A,E
Question # 2
Answer: C
Question # 3
Answer: A
Question # 4
Answer: E
Question # 5
Answer: A

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