Oracle 1z1-830 : Java SE 21 Developer Professional

Exam Code: 1z1-830

Exam Name: Java SE 21 Developer Professional

Updated: Aug 19, 2026

Q & A: 85 Questions and Answers

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Oracle 1z1-830 Exam Syllabus Topics:

SectionWeightObjectives
Topic 1: Concurrency and Multithreading10%- Thread lifecycle, Runnable, Callable, ExecutorService, virtual threads
- Synchronization, locks, concurrent collections, thread safety
Topic 2: Controlling Program Flow10%- Loops: for, enhanced for, while, do-while, break, continue, return
- Decision constructs: if-else, switch expressions and statements, pattern matching
Topic 3: 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
Topic 4: Advanced Features and Annotations3%- Generics, type parameters, wildcards, type erasure
- Annotations, built-in annotations, custom annotations
Topic 5: Java I/O and Localization5%- File I/O, NIO.2, streams, readers/writers, serialization
- Resource bundles, locale, formatting messages, numbers, dates
Topic 6: Handling Exceptions8%- Create and use custom exceptions, throw, throws
- Exception hierarchy, try-catch-finally, multi-catch, try-with-resources
Topic 7: Modules and Packaging5%- Module system: module-info.java, exports, requires, provides, uses
- Create and use JAR files, modular and non-modular builds
Topic 8: Functional Programming and Streams15%- Optional class, primitive streams
- Stream API: create, intermediate/terminal operations, parallel streams, grouping, partitioning
- Lambda expressions, functional interfaces, method references
Topic 9: Using Object-Oriented Concepts20%- Enums, nested classes, local variable type inference
- Classes, records, objects, constructors, initializers, methods, fields, encapsulation
- Overloading, overriding, Object class methods, immutable objects
- Inheritance, abstract classes, sealed classes, interfaces, polymorphism
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
Deque<Integer> deque = new ArrayDeque<>();
deque.offer(1);
deque.offer(2);
var i1 = deque.peek();
var i2 = deque.poll();
var i3 = deque.peek();
System.out.println(i1 + " " + i2 + " " + i3);
What is the output of the given code fragment?

A) 2 2 1
B) 1 1 2
C) 1 1 1
D) 1 2 1
E) 1 2 2
F) 2 1 1
G) 2 1 2
H) An exception is thrown.
I) 2 2 2


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


3. Which of the following doesnotexist?

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


4. Given:
java
LocalDate localDate = LocalDate.of(2020, 8, 8);
Date date = java.sql.Date.valueOf(localDate);
DateFormat formatter = new SimpleDateFormat(/* pattern */);
String output = formatter.format(date);
System.out.println(output);
It's known that the given code prints out "August 08".
Which of the following should be inserted as the pattern?

A) MM dd
B) MMM dd
C) MM d
D) MMMM dd


5. Given:
java
import java.io.*;
class A implements Serializable {
int number = 1;
}
class B implements Serializable {
int number = 2;
}
public class Test {
public static void main(String[] args) throws Exception {
File file = new File("o.ser");
A a = new A();
var oos = new ObjectOutputStream(new FileOutputStream(file));
oos.writeObject(a);
oos.close();
var ois = new ObjectInputStream(new FileInputStream(file));
B b = (B) ois.readObject();
ois.close();
System.out.println(b.number);
}
}
What is the given program's output?

A) 1
B) ClassCastException
C) 2
D) Compilation fails
E) NotSerializableException


Solutions:

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

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