Java MCQs

Question 1

What is the purpose of the 'final' keyword when applied to a variable in Java?

Accepted Answer

It prevents the variable from being reassigned after its initial value is set

Answer

It makes the variable accessible from any class

Answer

It automatically initializes the variable to zero

Answer

It marks the variable for garbage collection

Question 2

What is method overloading in Java?

Accepted Answer

Defining multiple methods in the same class with the same name but different parameter lists

Answer

Redefining a parent class method in a subclass with the same signature

Answer

Calling a method from within itself

Answer

Declaring a method as static

Question 3

How does method overriding differ from method overloading?

Accepted Answer

Overriding redefines a method inherited from a superclass with the same signature, while overloading creates methods with the same name but different parameters

Answer

Overriding happens at compile time, overloading happens at runtime

Answer

Overriding requires static methods, overloading requires instance methods

Answer

There is no meaningful difference between the two

Question 4

What does the 'static' keyword mean when applied to a method in Java?

Accepted Answer

The method belongs to the class rather than any specific instance and can be called without creating an object

Answer

The method cannot be called by any subclass

Answer

The method automatically runs when the program starts

Answer

The method can only be called once during the program's execution

Question 5

What is the purpose of a constructor in Java?

Accepted Answer

To initialize a new object when it is created

Answer

To destroy an object when it is no longer needed

Answer

To define the class's access modifier

Answer

To declare static variables for the class

Question 6

What is the difference between '==' and the equals() method when comparing Java objects?

Accepted Answer

'==' compares object references, while equals() compares the actual content unless overridden

Answer

'==' compares content, while equals() compares references

Answer

Both always compare content in exactly the same way

Answer

'==' only works on primitive types and cannot be used with objects

Question 7

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

Accepted Answer

It refers to the current instance of the class in which it is used

Answer

It refers to the parent class of the current object

Answer

It creates a new object of the class

Answer

It marks a variable as constant

Question 8

What happens when an array index is accessed that is outside the bounds of the array in Java?

Accepted Answer

An ArrayIndexOutOfBoundsException is thrown at runtime

Answer

The program silently returns null

Answer

The compiler prevents the code from building

Answer

The array automatically resizes to accommodate the index

Question 9

What is autoboxing in Java?

Accepted Answer

The automatic conversion between a primitive type and its corresponding wrapper class

Answer

The process of converting an object to a String

Answer

A technique for compressing memory usage of arrays

Answer

The automatic conversion between two unrelated primitive types

Question 10

What is the key difference between an abstract class and an interface in Java, in terms of state?

Accepted Answer

An abstract class can hold instance fields with state, while a traditional interface cannot

Answer

An interface can hold instance fields with state, while an abstract class cannot

Answer

Neither can hold any fields at all

Answer

Both behave identically in every respect

Question 11

What is the purpose of the 'super' keyword in Java?

Accepted Answer

To refer to the immediate parent class and access its members or constructor

Answer

To refer to the current object itself

Answer

To mark a class as final

Answer

To declare a method as abstract

Question 12

What is a NullPointerException typically caused by?

Accepted Answer

Attempting to call a method or access a field on a reference that points to null

Answer

Dividing an integer by zero

Answer

Trying to cast an object to an incompatible type

Answer

Accessing an array index beyond its length

Question 13

What is the purpose of garbage collection in Java?

Accepted Answer

To automatically reclaim memory occupied by objects that are no longer reachable by the program

Answer

To automatically delete unused classes at compile time

Answer

To compress the size of the compiled bytecode

Answer

To clean up unused import statements

Question 14

Which access modifier makes a member accessible only within its own class?

Accepted Answer

private

Answer

public

Answer

protected

Answer

default (package-private)

Question 15

What is the difference between StringBuilder and String in Java?

Accepted Answer

StringBuilder is mutable and can be changed after creation, while String is immutable

Answer

String is mutable, while StringBuilder is immutable

Answer

Both are immutable and behave identically

Answer

StringBuilder can only store numbers, not text

Question 16

What does the 'instanceof' operator check in Java?

Accepted Answer

Whether an object is an instance of a specific class or a class that implements a specific interface

Answer

Whether two variables reference the exact same object

Answer

Whether a variable has been initialized

Answer

Whether a class is declared as final

Question 17

What is the purpose of a try-with-resources statement in Java?

Accepted Answer

To automatically close resources like files or streams once the try block finishes, without needing an explicit finally block

Answer

To retry a failed operation automatically a fixed number of times

Answer

To catch multiple unrelated exceptions in a single catch block

Answer

To declare a resource as immutable

Question 18

What does the term 'immutable' mean when describing the String class in Java?

Accepted Answer

Once a String object is created, its contents cannot be changed

Answer

A String can be changed but only by the same thread that created it

Answer

A String cannot be passed as a method argument

Answer

A String automatically becomes uppercase after creation

Question 19

What is the default access modifier in Java when no modifier is explicitly specified?

Accepted Answer

Package-private, meaning accessible only within the same package

Answer