Core Java Quiz

Correct Answers: 0
Incorrect Answers: 0

1. What is garbage collection in Java?

The process of reclaiming memory from objects that are no longer in use

The process of compiling Java code

The process of deleting files from the system

The process of handling exceptions

2. Which of the following is a root of the garbage collection process in Java?

Local variables

Static fields

Active threads

All of the above

3. What is the purpose of the finalize() method in Java?

To allocate memory for an object

To create a new thread

To release resources before an object is garbage collected

To explicitly delete an object

4. Which garbage collector is designed for low-latency applications?

G1 Garbage Collector

Concurrent Mark-Sweep (CMS) Collector

Serial Garbage Collector

Parallel Garbage Collector

5. What is a memory leak in Java?

When objects are not properly released from memory

When too many threads are created

When memory is allocated but not used

When an application uses more memory than it needs

6. Which of the following is NOT a type of garbage collector in Java?

Mark-and-sweep

Generational Garbage Collector

Stack Garbage Collector

Reference counting

7. What does the JVM use to track the objects that need to be garbage collected?

Reference counting

Strong references

Weak references

All of the above

8. What is the primary goal of the Java memory model?

To optimize memory usage

To provide a consistent view of memory

To allow multiple threads to access memory simultaneously

To prevent memory leaks

9. Which of the following keywords can be used to prevent a class from being subclassed?

abstract

volatile

static

final

10. What is the purpose of the transient keyword in Java?

To prevent a variable from being modified

To mark a variable to be ignored during serialization

To indicate that a variable can change

To mark a variable for garbage collection

11. Which method is called when an object is no longer reachable?

dispose()

finalize()

destroy()

cleanUp()

12. What will happen if you call `System.gc()` in Java?

It suggests that the JVM performs garbage collection

It immediately performs garbage collection

It stops the program

It guarantees garbage collection

13. Which of the following types of references are eligible for garbage collection?

Strong references

Both B and C

Soft references

Weak references

14. What is the purpose of the Java Exception Handling mechanism?

To stop the program from executing

To ignore errors

To terminate the program abruptly

To catch and handle exceptions gracefully

15. What does the try-catch block do?

Handles exceptions at runtime

Catches all exceptions

Ignores exceptions

Terminates the program on an error

16. Which of the following statements is true about checked exceptions?

They must be handled or declared in the method signature

They are unchecked

They cannot be caught

They are not part of the Exception class

17. Which keyword is used to throw an exception manually?

finally

throw

throws

catch

18. Which of the following is not a primitive data type in Java?

float

String

boolean

int

19. What is the default value of a local variable in Java?

0

No default value

undefined

null

20. Which of these keywords is used to define an abstract class in Java?

final

abstract

extends

interface

21. Which method is used to start a thread in Java?

start()

init()

run()

execute()

22. Which of the following is a marker interface in Java?

Serializable

Cloneable

Runnable

All of the above

23. What is the main purpose of multithreading in Java?

To slow down the execution

To increase the memory usage

To use multiple CPUs efficiently

To allow multiple tasks to run concurrently

24. Which class is used to create a thread in Java?

Runnable

Process

Executor

Thread

25. Which method must be overridden to define the code that a thread will execute?

execute()

start()

run()

init()

26. What will happen if you call the `start()` method of a thread that is already running?

The thread will be paused

The thread will terminate

The thread will throw an IllegalThreadStateException

The thread will run again

27. Which of the following is the correct way to create a thread by implementing the Runnable interface?

Runnable r = new Runnable();

Runnable r = new MyRunnable();

Thread t = new Thread(new MyRunnable());

Thread t = new Thread();

28. What is the purpose of the `sleep()` method in Java?

To yield control to other threads

To create a new thread

To terminate a thread

To pause the current thread for a specified time

29. What is the effect of calling `join()` on a thread?

It throws an InterruptedException

It terminates the thread immediately

It pauses the current thread until the specified thread completes

It starts the specified thread

30. Which of the following methods is used to ensure mutual exclusion in multithreading?

volatile

synchronized

transient

final

31. What is a deadlock in Java?

When two or more threads are blocked forever

When a thread finishes its execution

When a thread is paused indefinitely

When a thread is waiting for another thread to finish

32. What does the `volatile` keyword do in Java?

It prevents thread interference

It ensures visibility of changes to variables across threads

It stops a thread from being paused

It makes a variable immutable

33. Which of the following can be used to create a thread pool in Java?

ThreadPoolExecutor

ExecutorService

Executors

All of the above

34. What is the output of the following code? `Thread t = new Thread(); t.start(); t.start();`?

It will run without any issues

It will pause the thread

It will throw an IllegalThreadStateException

It will terminate the thread

35. Which method is used to stop a thread safely in Java?

stop()

end()

terminate()

interrupt()

36. Which interface should be implemented to create a thread that can be interrupted?

Executor

Thread

Callable

Runnable

37. Which of the following is true about the `wait()` method?

It is used to pause the execution of a thread

It releases the lock on the object

It can only be called from a synchronized block

All of the above

38. What happens when `notify()` is called on an object?

It terminates the waiting thread

It wakes up all threads waiting on that object

It has no effect on threads

It wakes up a single thread that is waiting on that object

39. Which of the following methods can be used to check if a thread is alive?

isAlive()

checkAlive()

isRunning()

isActive()

40. Which of the following can be used to synchronize a block of code?

synchronized(lockObject)

synchronized(methodName)

Both A and B

synchronized(this)

41. Which interface is the root of the Java Collections Framework?

Set

Map

List

Collection

42. Which of the following classes implements the List interface?

LinkedHashMap

ArrayList

PriorityQueue

HashSet

43. Which collection class is synchronized?

TreeSet

Vector

HashMap

ArrayList

44. What is the output of the following code? `List<String> list = new ArrayList<>(); list.add("A"); list.add("B"); System.out.println(list.get(1));`

A

0

B

Error

45. Which of the following collections allows duplicate elements?

Set

List

Map

None of the above

46. Which class is used to implement a hash table in Java?

HashMap

TreeMap

LinkedHashMap

HashSet

47. What is the correct way to declare a HashSet in Java?

Set<String> set = new HashSet<>();

Both A and B

HashSet<String> set = new HashSet<>();

List<String> set = new HashSet<>();

48. Which of the following methods is used to remove all elements from a collection?

removeAll()

reset()

clear()

deleteAll()

49. What does the `contains()` method do in a collection?

Checks if a specific element is in the collection

Removes a specified element from the collection

Adds an element to the collection

Checks if the collection is empty

50. Which collection interface is not part of the Java Collections Framework?

Stack

Collection

Iterable

Deque

51. What is the default initial capacity of an ArrayList in Java?

0

20

10

5

52. Which collection is sorted by its natural ordering or by a comparator provided at collection creation time?

HashSet

TreeSet

ArrayList

LinkedHashMap

53. Which interface does the TreeMap implement?

List

Map

Set

Queue

54. Which of the following collections allows the insertion order to be maintained?

HashSet

LinkedHashMap

HashMap

TreeSet

55. Which method is used to get the number of elements in a collection?

size()

length()

getSize()

count()

56. What is the main advantage of using a LinkedList over an ArrayList?

Faster insertions and deletions

Better memory usage

Easier to implement

Faster retrieval of elements

57. What will be the output of the following code? `Set<Integer> set = new HashSet<>(); set.add(1); set.add(2); set.add(1); System.out.println(set.size());`

3

Error

2

1

58. Which of the following methods is used to retrieve and remove the head of a Queue?

remove()

pop()

poll()

dequeue()

59. What does the `toArray()` method return?

A new collection

A list of objects

A string representation of the collection

An array of objects

60. Which of these is not a keyword in Java?

private

Boolean

static

void

61. What is the range of a byte data type in Java?

0 to 255

-32768 to 32767

-256 to 255

-128 to 127

62. Which method is used to find the length of a string in Java?

length()

size()

getSize()

getLength()

63. What will be the output of 15 >>> 2 in Java?

15

4

2

3

64. Which of the following is a wrapper class in Java?

Integer

int

float

double

65. What is the purpose of the 'this' keyword in Java?

Refers to a method

Refers to the superclass

Refers to a static variable

Refers to the current object

66. What does the 'continue' statement do in a loop?

Skips the current iteration

Exits the loop

Restarts the loop

Jumps to the end of the loop

67. Which of these classes is used to handle input and output in Java?

Scanner

File

BufferedReader

All of the above

68. What will be the output of 10 + '20' + 30 in Java?

1030

60

None of the above

102030

69. Which keyword is used to prevent inheritance in Java?

private

final

abstract

static

70. Which of the following statements about Java arrays is true?

Arrays are dynamically sized

Arrays can be resized

Arrays are of fixed size

Arrays can store elements of different types

71. Which of these is not a valid data type in Java?

char

long

real

byte

72. Which method is used to get the runtime information about a Java application?

Runtime.getRuntime()

getEnv()

getRuntime()

System.getenv()

73. Which exception is thrown when an array is accessed with an illegal index in Java?

ArrayIndexOutOfBoundsException

IllegalArgumentException

IndexOutOfBoundsException

NullPointerException

74. Which of the following is not a Java feature?

Pointer-based

Architectural neutral

Portable

Dynamic

75. Which operator is used to allocate memory for an object in Java?

allocate

malloc

create

new

76. Which method must be implemented by a class implementing the Runnable interface?

run()

main()

execute()

start()

77. Which of the following is a reserved keyword in Java?

goto

None of the above

const

both A and B

78. What is the default access modifier for a class, method, or variable if no access modifier is specified?

public

private

protected

default (package-private)

79. Which method is called when an object is created in Java?

init()

new()

None of the above

constructor()

80. Which of the following is used to define a block of code that may throw an exception?

catch

finally

throw

try

81. What is the default value of an object reference variable in Java?

null

None of the above

undefined

0

82. Which of the following is not a loop structure in Java?

repeat

do-while

for

while

83. Which of the following methods is used to suspend a thread in Java?

pause()

sleep()

suspend()

wait()

84. Which of these statements about the 'final' keyword is true?

It can be used to prevent inheritance

It can be used to prevent method overriding

It can be used to define constants

All of the above

85. Which of the following is not a valid constructor declaration in Java?

private MyClass() {}

public MyClass() {}

protected MyClass() {}

void MyClass() {}

86. Which exception is thrown when a division by zero occurs in Java?

NullPointerException

ArithmeticException

IOException

ClassNotFoundException

87. Which of these is not a member of the java.lang package?

File

Integer

String

Math

88. Which access modifier makes a variable accessible only within its own class?

protected

default

private

public

89. What does the term 'method overloading' refer to in Java?

Multiple classes with the same name

Multiple constructors in a class

Multiple methods with the same name and different parameters

Multiple methods with different names

90. What is the purpose of the 'native' keyword in Java?

To define a method that is static

To define a method written in another language

None of the above

To define a method that is final

91. Which of the following is the base class for all exceptions in Java?

Error

Exception

RuntimeException

Throwable

92. Which method is used to convert a string into an integer in Java?

convertInt()

parseInt()

toString()

valueOf()

93. Which keyword is used to invoke the superclass constructor?

parent

extends

this

super

94. Which of the following is an example of a checked exception in Java?

IOException

NullPointerException

ArrayIndexOutOfBoundsException

ArithmeticException

95. Which of these keywords is used to manually throw an exception?

throws

throw

catch

finally

96. Which of these methods is used to register a thread for execution in Java?

run()

execute()

init()

start()

97. What does the 'transient' keyword do in Java?

Marks a method as final

Defines a variable as static

Indicates a method that runs in the background

Prevents serialization of a variable

98. Which of the following methods is defined in the Object class?

toString()

equals()

hashCode()

All of the above

99. Which of these cannot be used for a variable name in Java?

123myVariable

myVariable123

_myVariable

$myVariable

100. Which of the following is used to define an abstract method in Java?

native

abstract

interface

final

101. Which method is used to compare two strings for equality in Java?

equals()

==

compareTo()

compare()

102. Which of these is the correct way to create an array in Java?

int arr[5];

int[] arr = new int(5);

int arr[] = new int[5];

int[] arr = int[5];

103. Which operator in Java returns the remainder of a division?

%

*

+

/

104. Which of the following is the correct way to define a main method in Java?

public static void main(String args[])

static public void main(String args[])

public void static main(String args[])

public static void main()

105. Which of these is not a type of inheritance in Java?

Hierarchical

Multiple

Multilevel

Single

106. Which of the following is not a valid access modifier in Java?

private

default

protected

constant

107. Which method is used to terminate a thread in Java?

stop()

terminate()

exit()

kill()

108. Which of the following is not an interface in Java?

Runnable

Thread

Serializable

Cloneable

109. Which of the following is used to create a new object in Java?

new

allocate

make

initialize

110. Which method is automatically called during object creation in Java?

None of the above

constructor()

new()

init()

111. Which keyword is used to inherit a class in Java?

implements

super

extends

inherits

112. Which of these is a mutable class in Java?

Character

StringBuffer

String

Integer

113. Which of these is a correct way to create an infinite loop in Java?

for(;;)

while(true)

do{}while(true)

All of the above

114. Which of the following does not cause a thread to stop in Java?

yield()

sleep()

notify()

wait()

115. Which of these statements is true about a constructor in Java?

A constructor is called when an object is created

A constructor must return a value

A constructor can return null

A constructor cannot be overloaded

116. Which of these keywords is used to define a constant variable in Java?

final

static

immutable

const

117. Which of these classes is immutable in Java?

StringBuilder

StringBuffer

Integer

String

118. Which keyword is used to handle an exception in Java?

throw

throws

try

catch

119. Which method is used to find the length of an array in Java?

length

size()

getLength()

length()

120. Which method is used to check if two objects are equal in Java?

equals()

compareTo()

compare()

==

121. Which of the following types of exceptions can be thrown by the JVM?

Both

Checked exceptions

None

Unchecked exceptions

122. Which operator is used to concatenate two strings in Java?

.

+

||

&

123. Which of the following is used to terminate a switch statement in Java?

return

continue

break

exit

124. What is the default value of a boolean variable in Java?

true

0

false

null

125. Which of the following keywords is used to refer to the current object in a method?

object

self

this

super

126. Which of the following is not a reserved keyword in Java?

goto

null

true

strictfp

127. Which method is used to make a thread pause for a specific amount of time in Java?

stop()

pause()

wait()

sleep()

128. Which of the following is the size of an int in Java?

64 bits

8 bits

32 bits

16 bits

129. Which keyword is used to access the superclass constructor?

this

parent

super

base

130. Which method is used to terminate a program in Java?

System.exit()

terminate()

shutdown()

exit()

131. Which of the following is not a feature of Java?

Supports pointers

Multi-threaded

Object-oriented

Platform-independent

132. Which of the following is used to check whether a particular class implements an interface?

instanceof

implements

instance

extends

133. Which keyword is used to define a class in Java?

class

static

define

public

134. Which method is called when an object is destroyed in Java?

destroy()

delete()

finalize()

dispose()

135. Which of the following is a valid long literal in Java?

100000000l

100000000

100000000L

Both 100000000L and 100000000l

136. Which of the following will execute only once in a do-while loop, even if the condition is false?

switch

while

for

do

137. Which of the following is true about an abstract class in Java?

It cannot be instantiated

It must contain at least one abstract method

It can have constructors

All of the above

138. Which of the following methods is not present in the `Object` class?

equals()

toString()

sleep()

wait()

139. Which data type is used to store a sequence of characters in Java?

String

int

float

char

140. Which of the following is used for dynamic method dispatch in Java?

Inheritance

Encapsulation

Polymorphism

Abstraction

141. Which of these can be used to convert a string to a double in Java?

String.parseDouble()

Double.parseDouble()

Both Double.valueOf() and Double.parseDouble()

Double.valueOf()

142. Which of the following is a type of control flow statement in Java?

if

for

while

All of the above

143. Which of the following is a synchronized collection class in Java?

Vector

ArrayList

HashSet

HashMap

144. Which method is used to read a line of text from the console in Java?

System.in.read()

Both BufferedReader.readLine() and Scanner.nextLine()

Scanner.nextLine()

BufferedReader.readLine()

145. Which of the following is a final class in Java?

String

Exception

StringBuilder

Object

146. Which method is used to remove leading and trailing spaces from a string in Java?

trim()

strip()

substring()

stripLeading()

147. Which of the following is not a type of loop in Java?

do-while

foreach

for

while

148. Which of the following is true about the `static` keyword in Java?

It can be used with variables

It can be used with methods

It can be used with blocks

All of the above

149. Which of the following collections is ordered in Java?

HashSet

TreeSet

LinkedHashSet

Both TreeSet and LinkedHashSet

150. Which of the following is used to handle errors and exceptions in Java?

throw

try-catch

throws

All of the above

PreviousNext