1Z0-830 Practice Test 2 | Java SE 21 Developer

Question 1 MEDIUM

Which of the following var declarations are invalid? (Choose two.)

Select all that apply

var x = 10;
var y = 10, z = 20;
var a;
var b = new int[]{1,2};

var can declare only one variable per statement and must have an initializer. Multiple declarations and missing initialization are invalid. See more: Data Types & Variables

Question 2 MEDIUM

What is printed? int x = 2; int y = x++ + ++x; System.out.println(y);

6
7
8
Compilation fails

x++ returns 2, x becomes 3. ++x increments to 4 and returns 4. 2 + 4 = 6. See more: Data Types & Variables

Question 3 EASY

What is printed? for(int i=1;i<=3;i++){ if(i==2) continue; System.out.print(i); }

123
13
23
Compilation fails

When i==2, continue skips printing. Output: 13. See more: Control Flow

Question 4 MEDIUM

Which of the following can be overridden?

private method
static method
final method
non-final instance method

Only non-final instance methods can be overridden. Private and static are not overridden; final cannot be overridden. See: Object-Oriented Approach ->Overriding Rules

Question 5 EASY

Which exception must be declared or caught?

NullPointerException
IllegalArgumentException
IOException
RuntimeException

IOException is checked and must be handled or declared. See more: Exception Handling

Question 6 EASY

Which Set implementation maintains insertion order?

HashSet
TreeSet
LinkedHashSet
ConcurrentSkipListSet

LinkedHashSet preserves insertion order. See: Arrays & Collections ->Collections

Question 7 MEDIUM

Which operation is lazy?

forEach()
count()
map()
collect()

map() is an intermediate lazy operation. Terminal operations trigger execution. See more: Streams & Lambdas

Question 8 MEDIUM

Which statement makes a service available in module-info.java?

requires
exports
provides ... with
opens

provides ... with declares service implementation. See: Packaging & Deployment ->ServiceLoader

Question 9 EASY

Which class executes tasks asynchronously?

Thread
ExecutorService
Runnable
Callable

ExecutorService manages asynchronous execution. See more: Concurrency

Question 10 EASY

Which method writes bytes to a file?

Files.write()
Files.readAllLines()
Path.of()
Files.list()

Files.write(Path, byte[]) writes bytes. See more: Java I/O API

Question 11 MEDIUM

Which method creates a PreparedStatement?

Connection.createStatement()
Connection.prepareStatement()
Statement.prepare()
DriverManager.prepare()

prepareStatement() creates precompiled SQL statement. See more: JDBC

Question 12 EASY

Which class formats dates in modern Java API?

SimpleDateFormat
DateFormat
DateTimeFormatter
Calendar

DateTimeFormatter is part of java.time API. See more: Localization

Question 13 MEDIUM

Which is true about sealed classes?

They prevent all subclassing
They allow only permitted subclasses
They require abstract methods
They cannot be public

Sealed classes restrict subclassing to permitted types. See more: Java 21 New Features

Question 14 EASY

What is printed? String s = "Java"; System.out.println(s.repeat(2));

JavaJava
Java2
Compilation fails
Java Java

repeat(2) repeats the string twice. Output: JavaJava See more: Data Types & Variables

Question 15 MEDIUM

Which primitive type cannot be implicitly widened to long?

byte
short
int
char

char can be widened, but exam trick: char is unsigned 16-bit and can widen to int and long. However in numeric promotion contexts confusion occurs - the only correct implicit widening set excludes boolean. Since boolean is not listed, all listed types widen. Correct answer here is trick-based: char is widened differently but still valid. (For exam caution.) See more: Data Types & Variables

Question 16 EASY

Which statement exits the entire loop?

continue
break
return
yield

break exits the loop completely. See more: Control Flow

Question 17 EASY

Which modifier allows access within same package only?

public
protected
private
default

Default (package-private) allows access within same package. See: Object-Oriented Approach ->Access Modifiers

Question 18 EASY

Which keyword is used to implement an interface?

extends
implements
inherits
super

implements is used when a class implements an interface. See: Object-Oriented Approach ->Interfaces

Question 19 EASY

Which statement creates a custom exception?

class MyEx extends Exception {}
class MyEx implements Exception {}
class MyEx throws Exception {}
class MyEx inherits Exception {}

Custom exceptions extend Exception or RuntimeException. See more: Exception Handling

Question 20 MEDIUM

Which Map allows one null key?

HashMap
Hashtable
TreeMap
ConcurrentHashMap

HashMap allows one null key. Hashtable and ConcurrentHashMap do not. See: Arrays & Collections ->Map Implementations

Question 21 EASY

Which method removes and returns first element of Deque?

peek()
poll()
element()
getFirst()

poll() removes and returns head element. See: Arrays & Collections ->Deque

Question 22 EASY

Which functional interface takes no arguments and returns a value?

Supplier
Consumer
Function
Predicate

Supplier<T> supplies a value without input. See more: Streams & Lambdas

Question 23 EASY

Which Stream operation sorts elements?

map()
sorted()
filter()
limit()

sorted() sorts elements. See more: Streams & Lambdas

Question 24 MEDIUM

Which directive opens a package to reflection for specific modules?

exports
opens
opens to
requires

opens to allows reflection access to specific modules. See: Packaging & Deployment ->Modules

Question 25 MEDIUM

Which method causes a thread to give up CPU temporarily?

sleep()
yield()
join()
wait()

yield() hints scheduler to pause current thread. See more: Concurrency

Question 26 MEDIUM

Which keyword ensures visibility across threads?

synchronized
volatile
final
static

volatile guarantees visibility but not atomicity. See more: Concurrency

Question 27 EASY

Which class reads characters from file?

FileInputStream
FileReader
ObjectInputStream
Path

FileReader reads character data. See more: Java I/O API

Question 28 MEDIUM

Which method commits transaction manually?

commit()
close()
rollback()
flush()

commit() saves transaction changes. See more: JDBC

Question 29 EASY

Which method rolls back changes?

commit()
rollback()
execute()
save()

rollback() undoes transaction. See more: JDBC

Question 30 EASY

Which class represents currency?

Money
Currency
Locale
NumberFormat

Currency represents ISO currency codes. See more: Localization

Question 31 EASY

Which feature automatically generates equals and hashCode?

Enum
Record
Sealed
Module

Records auto-generate equals, hashCode, toString. See more: Java 21 New Features

Question 32 MEDIUM

Which pattern matching simplifies type casting?

switch
instanceof
record
lambda

instanceof pattern matching combines check and cast. See more: Java 21 New Features

Question 33 EASY

Which wrapper class corresponds to primitive int?

Int
Integer
Number
Long

Integer wraps primitive int. See more: Data Types & Variables

Question 34 MEDIUM

Which statement returns value from switch expression?

break
yield
return
continue

yield returns value in switch expression blocks. See more: Control Flow

Question 35 EASY

Which keyword prevents inheritance?

abstract
final
sealed
private

final prevents subclassing entirely. See: Object-Oriented Approach ->Class Design

Question 36 MEDIUM

Which method converts Stream to List?

toList()
collect(Collectors.toList())
Both
None

Both approaches create lists (Java 16+ supports toList()). See more: Streams & Lambdas

Question 37 EASY

Which operation limits number of elements?

limit()
skip()
distinct()
reduce()

limit(n) restricts stream size. See more: Streams & Lambdas

Question 38 EASY

Which tool compiles modules?

jlink
javac
jar
jdeps

javac compiles Java code including modules. See: Packaging & Deployment ->Tools

Question 39 MEDIUM

Which class supports parallel stream execution?

Thread
ForkJoinPool
Executor
Callable

Parallel streams use ForkJoinPool common pool. See more: Concurrency

Question 40 EASY

Which method checks if path exists?

Files.exists()
Path.exists()
File.existsPath()
Files.check()

Files.exists(Path) checks file existence. See more: Java I/O API

Question 41 EASY

Which primitive type stores true or false values?

int
boolean
char
byte

boolean represents true or false. It cannot be converted to numeric types. See more: Data Types & Variables

Question 42 MEDIUM

What is printed? int x = 1; System.out.println(x++ + x++);

2
3
4
Compilation fails

First x++ returns 1 (x becomes 2). Second x++ returns 2 (x becomes 3). 1 + 2 = 3. See more: Data Types & Variables

Question 43 EASY

Which loop is best used when the number of iterations is known?

while
do-while
for
foreach only

for loop is typically used when iteration count is known. See more: Control Flow

Question 44 EASY

Which keyword is used to call a superclass constructor?

this
parent
super
base

super() calls superclass constructor. See: Object-Oriented Approach ->Constructors & Inheritance

Question 45 EASY

Which interface method must be implemented?

default method
static method
abstract method
private method

Abstract methods must be implemented unless class is abstract. See: Object-Oriented Approach ->Interfaces

Question 46 EASY

Which block handles exceptions?

try
catch
finally
throw

catch handles thrown exceptions. See more: Exception Handling

Question 47 EASY

Which List implementation allows fast random access?

ArrayList
LinkedList
Vector
Stack

ArrayList supports O(1) index-based access. See: Arrays & Collections ->List Implementations

Question 48 EASY

Which collection does not allow duplicates?

List
Set
Map
Queue

Set does not allow duplicate elements. See: Arrays & Collections ->Collections Framework

Question 49 MEDIUM

Which method aggregates stream elements?

map()
filter()
reduce()
peek()

reduce() performs reduction operation on stream. See more: Streams & Lambdas

Question 50 EASY

Which interface consumes a value without returning anything?

Supplier
Function
Consumer
Predicate

Consumer<T> accepts input and returns void. See more: Streams & Lambdas

Question 51 MEDIUM

Which tool analyzes module dependencies?

javac
jlink
jdeps
jar

jdeps analyzes dependencies between modules. See: Packaging & Deployment ->Module Tools

Question 52 EASY

Which method blocks until a thread finishes?

sleep()
join()
wait()
yield()

join() waits for thread termination. See more: Concurrency

Question 53 MEDIUM

Which executor creates a single background thread?

Executors.newFixedThreadPool(1)
Executors.newSingleThreadExecutor()
Executors.newCachedThreadPool()
Executors.newWorkStealingPool()

newSingleThreadExecutor() creates exactly one worker thread. See more: Concurrency

Question 54 MEDIUM

Which method reads file content as Stream<String>?

Files.readAllLines()
Files.lines()
Path.readLines()
File.stream()

Files.lines(Path) returns Stream<String>. See more: Java I/O API

Question 55 EASY

Which object executes SQL statements?

Connection
Statement
ResultSet
Driver

Statement executes SQL queries. See more: JDBC

Question 56 MEDIUM

Which method disables auto-commit mode?

setAutoCommit(false)
disableCommit()
commit(false)
autoCommit(false)

setAutoCommit(false) enables manual transaction control. See more: JDBC

Question 57 MEDIUM

Which class formats compact numbers?

NumberFormat.getInstance()
NumberFormat.getCompactNumberInstance()
DecimalFormat
Formatter

getCompactNumberInstance() formats values like 1K, 1M. See more: Localization

Question 58 EASY

Which class represents time zone?

ZoneId
Locale
Currency
Period

ZoneId identifies time zones. See more: Localization

Question 59 MEDIUM

Which feature allows deconstruction in switch?

Records
Pattern matching
Modules
Generics

Pattern matching enables advanced switch matching. See more: Java 21 New Features

Question 60 MEDIUM

Which modifier must permitted subclasses declare?

public only
final/sealed/non-sealed
abstract only
static

Permitted subclasses must declare final, sealed, or non-sealed. See more: Java 21 New Features

Question 61 EASY

Which keyword allows a class to inherit from only one class?

implements
extends
super
abstract

Java supports single inheritance using extends. See: Object-Oriented Approach ->Inheritance

Question 62 MEDIUM

Which Map sorts by key naturally?

HashMap
TreeMap
LinkedHashMap
Hashtable

TreeMap sorts keys using natural ordering. See: Arrays & Collections ->Sorted Collections

Question 63 EASY

Which method removes duplicates in a stream?

filter()
distinct()
reduce()
peek()

distinct() removes duplicate elements. See more: Streams & Lambdas

Question 64 MEDIUM

Which concurrent collection uses lock-free segmentation?

HashMap
ConcurrentHashMap
TreeMap
ArrayList

ConcurrentHashMap uses segmented locking / CAS for concurrency. See more: Concurrency

Question 65 EASY

Which statement rethrows an exception?

throw e;
throws e;
catch e;
retry e;

throw e; rethrows the exception. See more: Exception Handling

Question 66 MEDIUM

Which tool creates custom runtime images?

javac
jlink
jar
jdeps

jlink builds optimized runtime images for modular apps. See: Packaging & Deployment ->Deployment Tools

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