Java MCQ Question for Answer
QUESTION - 1
1. What does encapsulation mean in java?
a) Grouping data and methods
b) Hiding data
c) Inheritance
d) Overloading
Ans : Hiding data
Reason : encapsulation is used for hide the data from user setter function is hide function in setter function data is visible
Example :
public class Student {
// private data - encapsulated
private String name;
// public getter for name
public String getName() {
return name;
}
// public setter for name
public void setName(String name) {
this.name = name;
}
}
2. Which keyword prevents method overriding?
a) static
b) private
c) final
d) super
Answer : Final
Reason : This method is complete and should not be changed by subclasses.
Example :
class Parent {
public final void show() {
System.out.println("This is a final method.");
}
}
class Child extends Parent {
public void show() {
System.out.println("Trying to override.");
}
}
3. What is the purpose of the 'new' keyword?
a) Create class
b) Create object
c) Create variable
d) Call method
Answer : Create object
Reason : The new keyword in Java is used to create an object (instance) of a class
Example :
class Car {
void display() {
System.out.println("This is a car.");
}
}
public class Main {
public static void main(String[] args) {
// Creating an object of Car using 'new'
Car myCar = new Car();
myCar.display();
}
}
4. Which of the following is used for polymorphism?
a) Method overloading
b) Variables
c) final keyword
d) Static blocks
Answer : Method overloading
Reason :
Method Overloading and Method Overriding
Both are key ways to achieve polymorphism in Java
Method Overloading allows us to define multiple methods with the same name but different parameters within a class. This difference can be in the number of parameters, the types of parameters, or the order of those parameters
Example :
class MathUtils {
// Overloaded methods
int add(int a, int b) {
return a + b;
}
double add(double a, double b) {
return a + b;
}
}
public class Main {
public static void main(String[] args) {
MathUtils m = new MathUtils();
System.out.println(m.add(5, 10)); // Outputs: 15
System.out.println(m.add(2.5, 3.2)); // Outputs: 5.7
}
}
5. Which data type is used to store text?
a) int
b) char
c) String
d) Boolean
Answer : String
Reason :
In Java, the String data type is used to store a sequence of characters, which means it's the correct choice for storing text.
int stores integers (numbers).
char stores a single character.
boolean stores either true or false.
String stores a group of characters — i.e., text like names, sentences, etc.
Example :
public class Main {
public static void main(String[] args) {
String message = "Hello, Java!";
System.out.println(message); // Output: Hello, Java!
}
}
6. How do you access a static method?
a) Using object
b) Using class name
c) Using variable
d) Can't access
Answer : Using class name
Reason :
In Java, a static method belongs to the class itself, not to any object instance.
That means you can (and should) access it using the class name, without creating an object.
Example:
class Greeting {
// static method
public static void sayHello() {
System.out.println("Hello, world!");
}
}
public class Main {
public static void main(String[] args) {
// Accessing the static method using class name
Greeting.sayHello(); // Output: Hello, world!
}
}
7. What is the size of an int in Java?
a) 2 bytes
b) 4 bytes
c) 8 bytes
d) 1 byte
Answer : 4 bytes
Reason : In Java, the int data type is always a 32-bit signed integer, regardless of the operating system or processor.
. 1 byte = 8 bits
. 4 bytes = 32 bits
It can store values from -2,147,483,648 to 2,147,483,647.
Example:
public class Main {
public static void main(String[] args) {
int number = 100;
System.out.println("Value: " + number); // Output: Value: 100
}
}
8. What is the default value of a boolean variable?
a) true
b) false
c) 0
d) null
Answer : false
Reason:
In Java, if a boolean variable is declared as a class-level (instance) variable and not explicitly initialized, it is automatically assigned the default value false.
1) true is a possible value, but not the default.
2) 0 is for numeric types like int.
3) null is for object references (like String, Integer).
Example:
public class Test {
boolean isActive; // not initialized
public void showStatus() {
System.out.println("isActive: " + isActive);
}
public static void main(String[] args) {
Test t = new Test();
t.showStatus(); // Output: isActive: false
}
}
9. Which keyword is used to stop inheritance?
a) static
b) private
c) final
d) super
Answer: final
Reason:
In Java, the final keyword is used to prevent a class from being inherited (i.e., extended).
If a class is declared as final, no other class can subclass or extend it.
Example:
final class Vehicle {
void display() {
System.out.println("This is a vehicle.");
}
}
// This will cause an error:
// class Car extends Vehicle {} Not allowed
or
// Main class
class GFG {
// Main driver method
public static void main(String args[])
{
// Final primitive variable
final int i = 10;
i = 30;
// Error will be generated above
}
}
10. How many objects are created in: Student s1 = new Student();?
a) 1
b) 0
c) 2
d) None
Answer: 1
Reason:
In the statement Student s1 = new Student();, one object is created. The new Student() part creates a new instance of the Student class, and s1 is a reference variable that stores a reference to this newly created object.
. The new Student() part creates one object in memory (on the heap).
. The s1 is just a reference variable that points to that object.
. So only one actual object is created
Example:
class Student {
Student() {
System.out.println("Student object created!");
}
}
public class Main {
public static void main(String[] args) {
Student s1 = new Student(); // Output: Student object created!
}
}
QUESTION - 2
1. Which of the following is used for polymorphism?
a) Method overloading
b) Variables
c) final keyword
d) Static blocks
Answer: Method overloading
Reason :
Polymorphism is a concept in object-oriented programming that allows objects to take on many forms. One type of polymorphism is compile-time polymorphism, which is achieved using method overloading.
- Method Overloading means defining multiple methods with the same name but different parameters within the same class.
- It helps the program decide which method to invoke at compile time based on the method signature (number and type of parameters).
Example:
class PolymorphismExample {
void display() {
System.out.println("No parameters");
}
void display(String name) {
System.out.println("Name: " + name);
}
void display(int age) {
System.out.println("Age: " + age);
}
public static void main(String[] args) {
PolymorphismExample obj = new PolymorphismExample();
obj.display(); // Calls method with no parameters
obj.display("Alice"); // Calls method with String parameter
obj.display(25); // Calls method with int parameter
}
}
or
class Calculator {
// Method 1: Adds two integers
int add(int a, int b) {
return a + b;
}
// Method 2: Adds three integers
int add(int a, int b, int c) {
return a + b + c;
}
// Method 3: Adds two double numbers
double add(double a, double b) {
return a + b;
}
public static void main(String[] args) {
Calculator calc = new Calculator();
System.out.println("Sum of 2 and 3: " + calc.add(2, 3));
System.out.println("Sum of 1, 2 and 3: " + calc.add(1, 2, 3));
System.out.println("Sum of 2.5 and 3.5: " + calc.add(2.5, 3.5));
}
}
2. How do you create an object in Java?
a) ClassName obj = new ClassName();
b) new ClassName();
c) ClassName();
d) Object obj = ClassName();
Answer: ClassName obj = new ClassName();
Reason:
In Java, to create an object
-
Declare a reference variable of the class type.
-
Instantiate the object using the
newkeyword. -
Assign the new object to the reference variable.
This is the correct way to create an object in Java.
It means:-
ClassName– the type of object you want. -
obj– the name of the object. -
new– keyword to create a new object. -
ClassName()– calls the class constructor.
-
Example:
class Car {
void drive() {
System.out.println("Driving...");
}
public static void main(String[] args) {
Car myCar = new Car(); // Object creation
myCar.drive(); // Calling method using the object
}
}
or
class Person {
String name;
int age;
// Constructor with parameters
Person(String name, int age) {
this.name = name;
this.age = age;
}
// Method to display person info
void display() {
System.out.println("Name: " + name);
System.out.println("Age: " + age);
}
public static void main(String[] args) {
// Creating an object with name and age
Person obj = new Person("Alice", 25);
obj.display();
}
}
3. Which keyword is used to define a constant value in Java?
a) static
b) final
c) const
d) constant
Answer: final
Reason :
In Java, the
final keyword is used to define a constant — a variable whose value cannot be changed after it's assigned.The final keyword is used to define a constant value in Java. When a variable is declared with the final keyword, its value cannot be changed after it has been initialized. This makes it a constant.
Example :
final using not changed after it's assigned
final int MAX_VALUE = 100;
4. Which keyword is used to inherit a class?
a) implements
b) extends
c) inherits
d) super
d) super
Answer: extends
Reason: In Java, the
extends keyword is used when one class inherits another class.Example:
class Animal {
void sound() {
System.out.println("Animal makes a sound");
}
}
class Dog extends Animal {
void bark() {
System.out.println("Dog barks");
}
}
5. What is inheritance in Java?
a) Reusing fields and methods of another class
b) Creating private variables
c) Declaring static methods
d) Defining interfaces
Answer: Reusing fields and methods of another class
Reason:
Inheritance in Java means one class gets the properties and behaviors (fields and methods) of another class. It helps in code reuse.
Example:
// Superclass (Parent)
class Animal {
void eat() {
System.out.println("Animal is eating...");
}
void sleep() {
System.out.println("Animal is sleeping...");
}
}
// Subclass (Child) - Inherits from Animal
class Dog extends Animal {
void bark() {
System.out.println("Dog is barking!");
}
}
public class Main {
public static void main(String[] args) {
Dog myDog = new Dog();
// Inherited methods (from Animal)
myDog.eat();
myDog.sleep();
// Child class method
myDog.bark();
}
}
or
class Animal {
void eat() {
System.out.println("This animal eats food");
}
}
class Dog extends Animal {
void bark() {
System.out.println("The dog barks");
}
}
public class Main {
public static void main(String[] args) {
Dog d = new Dog();
d.eat(); // Inherited method
d.bark(); // Dog's own method
}
}
6. Which data type is used to store text?
a) int
b) Char
c) String
d) Boolean
Answer: String
Reason :
In Java, the
String data type is used to store text — a sequence of characters. Use
String to store text in Java.Example:
String name = "Alice";
System.out.println(name);
7. Which keyword is used to stop inheritance?
a) static
b) private
c) final
d) super-That
Answer: Final
Reason:
In Java, the
If you make a class
final keyword is used to stop inheritance.If you make a class
final, no other class can extend it.Example:
final class Animal {
void sound() {
System.out.println("Animal sound");
}
}
// This will cause an error
class Dog extends Animal { // ❌ Error: cannot inherit from final class
void bark() {
System.out.println("Dog barks");
}
}
8. What does polymorphism allow?
a) One method with many forms
b) One class only
c) Data hiding
d) object creation
Answer: One method with many forms
Reason:
Polymorphism in Java means "many forms"
It allows a method to behave differently based on input or object type.
It allows a method to behave differently based on input or object type.
Example:
class Animal {
void sound() {
System.out.println("Animal sound");
}
}
class Dog extends Animal {
void sound() {
System.out.println("Dog barks");
}
}
class Cat extends Animal {
void sound() {
System.out.println("Cat meows");
}
}
public class Main {
public static void main(String[] args) {
Animal a;
a = new Dog();
a.sound(); // Dog barks
a = new Cat();
a.sound(); // Cat meows
}
}
or
class Animal {
void sound() {
System.out.println("Animal makes a sound");
}
}
class Dog extends Animal {
@Override
void sound() {
System.out.println("Dog barks");
}
}
public class Main {
public static void main(String[] args) {
Animal a = new Dog(); // Parent class reference, child class object
a.sound(); // Calls Dog's version of sound()
}
}
9. What is a setter method used for?
a) Assign values
b) Retrieve values
c) Print
d) Compile
Answer: Assign values
Reason:
A setter method is used to assign values to a class's private variables.
Setter → set/assign values
Getter → get/retrieve values
Example:
class Person {
private String name;
// Setter method
public void setName(String newName) {
name = newName;
}
// Getter method (just for reference)
public String getName() {
return name;
}
}
public class Main {
public static void main(String[] args) {
Person p = new Person();
p.setName("Alice"); // Using setter to assign value
System.out.println(p.getName()); // Output: Alice
}
}
10. What does method overriding mean?
a) Redefining inherited method
b) Duplicating method
c) Creating error
d) Calling constructor
Answer: Redefining inherited method
Reason:
Method overriding, in object-oriented programming (OOP), is a mechanism where a subclass (child class) provides its own specific implementation of a method that is already defined in its superclass (parent class).
Method overriding means a subclass provides its own version of a method that is already defined in its parent class.
Example:
class Animal {
void sound() {
System.out.println("Animal makes a sound");
}
}
class Dog extends Animal {
@Override
void sound() {
System.out.println("Dog barks");
}
}
public class Main {
public static void main(String[] args) {
Animal a = new Dog(); // Creating a Dog object
a.sound(); // Calls Dog's version of sound (method overriding)
}
}
or
class Animal {
void sound() {
System.out.println("Animal makes a sound");
}
}
class Dog extends Animal {
@Override
void sound() {
System.out.println("Dog barks");
}
}
public class Main {
public static void main(String[] args) {
Animal a = new Dog();
a.sound(); // Calls Dog's sound method
}
}
Question - 3
1. Which of the frilowing is a valid class declaration?
a) class my-class (
b) Class MyClass()
c) class MyClass()
d) myclass class()
Answer: lass MyClass()
Reason:
class Keyword:
This keyword is mandatory and indicates that you are declaring a class.
Example:
// Class Declaration
class Student
{
class body
}
// Class Declaration
class Test
{
public static void main(String[] args)
{
System.out.println("Class File Structure");
}
}
or
class MyClass {
// class body
}
2. What is the default access modifier for class members in Java?
a) private
b) public
c) default
d) protected
Answer: default
Reason:
When no access modifier is specified, the member has package-private (default) access, meaning it is accessible within the same package.
Example:
// File: Animal.java
package zoo;
class Animal {
int age = 5; // default access modifier
void displayAge() { // also has default access
System.out.println("Age: " + age);
}
}
// File: ZooTest.java
package zoo;
public class ZooTest {
public static void main(String[] args) {
Animal a = new Animal();
a.displayAge(); // ✅ Works fine, same package
}
}
or
error
// File: SafariTest.java
package safari;
import zoo.Animal;
public class SafariTest {
public static void main(String[] args) {
Animal a = new Animal(); // ❌ Error: Animal is not public
a.displayAge(); // ❌ Error: displayAge() not visible
}
}
3. Which keyword is used to define a constant value?
a) static
b) final
c) const
d) constant
Answer: final
Reason :
In Java, the
final keyword is used to define a constant — a variable whose value cannot be changed after it's assigned.The final keyword is used to define a constant value in Java. When a variable is declared with the final keyword, its value cannot be changed after it has been initialized. This makes it a constant.
Example :
final using not changed after it's assigned
final int MAX_VALUE = 100;
4. What will be the output of System.out.printin(10+"Java")?
a) 10Java
b) Java 10
c) Error
d) 10 Java
Answer: 10java
Reason:
The
+ operator combines (concatenates) the number 10 and the string "Java" into a new string.Example:
System.out.println(10 + "Java"); // Output: 10Java
or
// Declare a class named ClassName
class ClassName {
// Declare the main method (starting point)
public static void main(String[] args) {
// Print 10 concatenated with "Java"
System.out.println(10 + "Java");
}
}
5. An object in Java is created using:
a) method
b) constructor
c) interface
d) class loader
Answer: constructor
Reason:
A constructor is a special method used to instantiate (create) an object.
Example:
MyClass obj = new MyClass();
or
class GFG {
// Declaring and initializing string
// Custom input string
String name = "GeeksForGeeks";
// Main driver method
public static void main(String[] args)
{
// As usual and most generic used we will
// be creating object of class inside main()
// using new keyword
GFG obj = new GFG();
// Print and display the object
System.out.println(obj.name);
}
}
6. What does the static keyword indicate?
a) Constant value
b) Belongs to instance
c) Belongs to class
d) Can't be accessed
Answer: Belongs to class
Reason:
A
static member is shared across all instances and can be accessed without creating an objectExample:
class Test
{
// static method
static void m1()
{
System.out.println("from m1");
}
public static void main(String[] args)
{
// calling m1 without creating
// any object of class Test
m1();
}
}
or
class Test {
static int count = 0;
}
7. Which method is used to retrieve private variables?
a) getter
b) fetcher
c) scanner
d) retriever
Answer: getter
Reason:
The method used to retrieve private variables is called a getter.
In Java, private variables cannot be accessed directly from outside the class (this is part of the concept called encapsulation).
To safely access (read) the value of a private variable, we create a getter method.
A getter:
Is usually public.
Returns the value of the private variable.
Typically starts with the word get followed by the variable name in CamelCase.
Example:
private int age;
public int getAge() {
return age;
}
or
class Student {
// Private variable
private int age;
// Getter method to retrieve private variable
public int getAge() {
return age;
}
// Setter method (optional) to set private variable
public void setAge(int age) {
this.age = age;
}
}
class MainClass {
public static void main(String[] args) {
Student s = new Student();
s.setAge(20); // setting the age
System.out.println(s.getAge()); // getting the age
}
}
8. Java arrays are:
a) Dynamic
b) Objects
c) Functions
d) Variables
Answer: Objects
Reason:
In Java, arrays are treated as objects, no matter if they store primitive types (int, char, etc.) or objects (String, Integer, etc.).
This means arrays:
1. Are created on the heap memory.
2. Have a built-in .length property (not a method).
3. Can be used like any object — assigned, passed to methods, returned from methods.
Example:
Object type array (String)
public class StringArray {
public static void main(String[] args) {
String[] fruits = {"Apple", "Banana", "Mango"};
for (String fruit : fruits) {
System.out.println(fruit);
}
}
}
or
public class CheckObject {
public static void main(String[] args) {
int[] arr = new int[5];
System.out.println(arr instanceof Object); // true
}
}
9. What is the correct way to declare an array?
a) int arr-new int[5],
b) array arr new array(5);
c) int[] arr = 5;
d) int arr = new int[];
Answer: int arr = new int[5];
Reason:
The correct way to declare an array involves specifying the data type, the array name, and the size (number of elements) the array will hold. This is often done with the syntax: dataType[] arrayName = new dataType[size];.
Here's a breakdown of the process with examples:
1. Declaration (specifying the type and name):
dataType[] arrayName;
dataType: The type of data the array will hold (e.g., int, String, double, etc.).
arrayName: The name you choose for your array (e.g., myArray, numbers, names).
2. Initialization (allocating memory and potentially assigning values):
Option 1: Using the new keyword and size:
dataType[] arrayName = new dataType[size];
size: The number of elements the array will store.
Example: int[] numbers = new int[5]; (This declares an array named numbers to hold 5 integers)
Option 2: Initializing with values directly (shortcut for smaller arrays):
dataType[] arrayName = {value1, value2, ...};
Example: String[] names = {"Alice", "Bob", "Charlie"};
Example:
public class MyArray {
public static void main(String[] args) {
int[] arr = new int[5];
arr[0] = 10;
System.out.println(arr[0]); // Output: 10
}
}
or
// Declare an array to hold integers
int[] numbers;
// Create an array of size 5 (memory allocated)
numbers = new int[5];
// Initialize an array with some values
int[] scores = {85, 92, 78, 95, 89};
// Accessing an element (index starts from 0)
System.out.println(scores[0]); // Output: 85
10. Which OOP principle allows methods to behave differently based on parameters?
a) Encapsulation
b) Abstraction
c) Polymorphism
d) Inheritance
Answer: Polymorphism
Reason:
Polymorphism means "many forms". In Java, this allows:
Method Overloading – same method name, different parameter types.
Method Overriding – same method in a subclass behaves differently.
Example:
Method Overloading – same method name, different parameter types.
class Greet {
void sayHello() {
System.out.println("Hello!");
}
void sayHello(String name) {
System.out.println("Hello, " + name + "!");
}
}
public class Demo {
public static void main(String[] args) {
Greet g = new Greet();
g.sayHello(); // Output: Hello!
g.sayHello("Alice"); // Output: Hello, Alice!
}
}
or
Method Overriding – same method in a subclass behaves differently.
// Parent class
class Animal {
void sound() {
System.out.println("Animal makes a sound");
}
}
// Child class
class Dog extends Animal {
// Overriding the sound() method of Animal
@Override
void sound() {
System.out.println("Dog barks");
}
}
// Main class
public class TestOverride {
public static void main(String[] args) {
Animal myAnimal = new Animal();
myAnimal.sound(); // Output: Animal makes a sound
Dog myDog = new Dog();
myDog.sound(); // Output: Dog barks
Animal obj = new Dog();
obj.sound(); // Output: Dog barks (runtime polymorphism)
}
}
Question - 4
1. Which keyword is used to define a constant value in Java?
a) static
b) final
c) const
d) constant
Answer: final
Reason :
In Java, the
final keyword is used to define a constant — a variable whose value cannot be changed after it's assigned.The final keyword is used to define a constant value in Java. When a variable is declared with the final keyword, its value cannot be changed after it has been initialized. This makes it a constant.
Example :
final using not changed after it's assigned
final int MAX_VALUE = 100;
2. What does 'static' mean in Java?
a) Belongs to object
b) Belongs to class
c) Constant
d) Variable
Answer: Belongs to class
Reason:
When a variable or method is declared
This means you don't need to create an object to access it.
static, it belongs to the class, not to any specific object.This means you don't need to create an object to access it.
Example:
class Example {
static int count = 0; // static variable
static void display() { // static method
System.out.println("Count is: " + count);
}
}
// Accessing without creating an object
Example.display();
3. How do you create an object in Java?
a) ClassName obj = new ClassName();
b) new
c) ClassName();
d) Object obj = ClassName();
nswer: ClassName obj = new ClassName();
Reason:
In Java, to create an object
Declare a reference variable of the class type.
Instantiate the object using the
newkeyword.Assign the new object to the reference variable.
This is the correct way to create an object in Java.
It means:ClassName– the type of object you want.obj– the name of the object.new– keyword to create a new object.ClassName()– calls the class constructor.
Example:
class Car {
void drive() {
System.out.println("Driving...");
}
public static void main(String[] args) {
Car myCar = new Car(); // Object creation
myCar.drive(); // Calling method using the object
}
}
or
class Person {
String name;
int age;
// Constructor with parameters
Person(String name, int age) {
this.name = name;
this.age = age;
}
// Method to display person info
void display() {
System.out.println("Name: " + name);
System.out.println("Age: " + age);
}
public static void main(String[] args) {
// Creating an object with name and age
Person obj = new Person("Alice", 25);
obj.display();
}
}
4. Which keyword is used to inherit a class?
a) implements
b) extends
c) inherits
d) super
Answer: extends
Reason:
In Java, inheritance is done using the
extends keywordExample:
class Animal {
void eat() { System.out.println("This animal eats food."); }
}
class Dog extends Animal {
void bark() { System.out.println("Dog barks."); }
}
5. Which method used is to access private variables?
a) getters
b) public
c) accessors
d) openers
Answer: getters
Reason :
Private variables can't be accessed directly. We create getter methods (and sometimes setters) to read them.
Private variables in Java are designed to be accessed only within the class in which they are declared. Direct access from outside the class is not allowed, ensuring data encapsulation and security.
However, there are two primary methods to indirectly access and modify private variables:
Getter and Setter Methods (Accessors and Mutators):
Getter methods: (also known as accessors) provide a way to retrieve the value of a private variable. They are typically public methods that return the variable's value.
Setter methods: (also known as mutators) allow you to modify the value of a private variable. They are typically public methods that take a new value as a parameter and update the variable.
Example:
class Person {
private String name;
public String getName() {
return name;
}
}
6. What is the return type of a constructor?
a) void
b) int
c) none
d) It has no return type
Answer: It has no return type
Reason:
No Return Type: Constructors do not have any return type, not even void. The main purpose of a constructor is to initialize the object, not to return a value. Automatically Called on Object Creation: When an object of a class is created, the constructor is called automatically to initialize the object's attributes
Example:
class Car {
Car() { // Constructor without return type
System.out.println("Car is created");
}
}
7. How do you declare an integer array?
a) int arr[] = new int[5];
b) arr int = new int[5];
c) int arr = int[5];
d) new int = arr[5];
Answer: int arr[] = new int[5];
Reason:
Reason:
The correct way to declare an array involves specifying the data type, the array name, and the size (number of elements) the array will hold. This is often done with the syntax: dataType[] arrayName = new dataType[size];.
Here's a breakdown of the process with examples:
1. Declaration (specifying the type and name):
dataType[] arrayName;
dataType: The type of data the array will hold (e.g., int, String, double, etc.).
arrayName: The name you choose for your array (e.g., myArray, numbers, names).
2. Initialization (allocating memory and potentially assigning values):
Option 1: Using the new keyword and size:
dataType[] arrayName = new dataType[size];
size: The number of elements the array will store.
Example: int[] numbers = new int[5]; (This declares an array named numbers to hold 5 integers)
Option 2: Initializing with values directly (shortcut for smaller arrays):
dataType[] arrayName = {value1, value2, ...};
Example: String[] names = {"Alice", "Bob", "Charlie"};
Example:
public class MyArray {
public static void main(String[] args) {
int[] arr = new int[5];
arr[0] = 10;
System.out.println(arr[0]); // Output: 10
}
}
or
// Declare an array to hold integers
int[] numbers;
// Create an array of size 5 (memory allocated)
numbers = new int[5];
// Initialize an array with some values
int[] scores = {85, 92, 78, 95, 89};
// Accessing an element (index starts from 0)
System.out.println(scores[0]); // Output: 85
8. which key word is used to inheritance?
a) static
b) private
c) final
d) super
Answer: final
Reason:
When you declare a class as
final, it cannot be extended by any other classSimilarly, if you mark a method as
final, it cannot be overridden by subclassesExample:
final class Vehicle {
void drive() {
System.out.println("Driving...");
}
}
// This will cause an error:
// class Car extends Vehicle { } // Error: Cannot inherit from final class
9. Which class is used for dynamic arrays in Java?
a) Array
b) List
c) ArrayList
d) DynamicArray
Answer: ArrayList
Reason:
In Java, the ArrayList class is the most commonly used class for implementing dynamic arrays. It belongs to the java.util package and provides a resizable array implementation of the List interface.
Example:
import java.util.ArrayList;
public class DynamicArrayExample {
public static void main(String[] args) {
ArrayList<Integer> numbers = new ArrayList<>();
numbers.add(10);
numbers.add(20);
numbers.add(30);
System.out.println(numbers); // Output: [10, 20, 30]
numbers.remove(1);
System.out.println(numbers); // Output: [10, 30]
}
}
10. What does the keyword 'this' refer to?
a) Current class
b) Parent class
c) New object
d) Static method
Answer: Current class
Reason:
this refers to the current object's instance — especially used when local variables hide instance variables.In Java, the this keyword refers to the current object within a class
Example:
class Student {
int age;
Student(int age) {
this.age = age; // this refers to the instance variable
}
}
Question - 5
1. What is method overloading?
a) Same method name, different parameters
b) Same class
c) Same variable
d) None
Answer: Same method name, different parameters
Reason:
Method overloading means having multiple methods with the same name but different parameter lists (different type, number, or order of parameters) within the same class.
Example:
class MathOperation {
int add(int a, int b) {
return a + b;
}
double add(double a, double b) {
return a + b;
}
}
2. What is the use of getter methods?
a) Retrieve values
b) Set values
c) Call methods
d) Run loops
Answer: Retrieve values
Reason:
Getter methods are used to get or retrieve the value of private fields from a class.
Example:
class Student {
private String name;
public String getName() {
return name;
}
}
3. What is the name of the method that runs when object is created?
a) init()
b) constructor
c) get()
d) new()
Answer: constructor
Reason:
In Java, the method that runs when an object is created is called a constructor
The constructor is a special method that automatically runs when an object of a class is created.
Example:
class Car {
Car() {
System.out.println("Car is created");
}
}
or
public class MyClass {
int x;
// Constructor with no arguments
public MyClass() {
x = 0; // Initialize x to 0
}
// Constructor with one argument
public MyClass(int value) {
x = value; // Initialize x to the given value
}
public static void main(String[] args) {
MyClass obj1 = new MyClass(); // Calls the no-argument constructor
MyClass obj2 = new MyClass(10); // Calls the one-argument constructor
System.out.println(obj1.x); // Output: 0
System.out.println(obj2.x); // Output: 10
}
}
4. What does JVM stand for?
a) Java Virtual Method
b) Java Variable Machine
c) Java Virtual Machine
d) Java Verified Machine
Answer: Java Virtual Machine
Reason:
JVM is responsible for running Java programs by converting bytecode into machine code at runtime.
Example:
When you run
java MyProgram, the JVM executes the compiled .class file5. Which symbol is used for comments in Java?
a) #
b) //
c)\
d) !!
Answer: //
Reason:
// is used for single-line comments in Java.Example:
// This is a comment
System.out.println("Hello");
6. Can we overload the constructor in Java?
a) Yes
b) No
c) Only once
d) Only for static class
Answer: Yes
Reason:
Yes, constructors in Java can be overloaded. This means you can have multiple constructors within the same class, as long as they have different parameter lists.
You can have multiple constructors with different parameter lists (constructor overloading).
Example:
class Box {
Box() { }
Box(int length) { }
Box(int length, int breadth) { }
}
7. What is the default value of a boolean variable?
a) true
b) false
c) 0
d) null
Answer: false
Reason: In Java, the default value for boolean fields is fasle.
Example:
class Test {
boolean flag;
public static void main(String[] args) {
Test t = new Test();
System.out.println(t.flag); // prints false
}
}
8. What is the output of: System.out.println(10 + "20");
a) 30
b) 1020
c) Error
d) 10 20
Answer: 1020
Reason:
Java reads from left to right;
10 is converted to string and concatenated with "20".Example: System.out.println(10 + "20"); // Output: 1020
9. What is a class in Java?
a) Blueprint
b) Object
c) Method
d) Variable
Answer: Blueprint
Reason:
A class is a blueprint or template for creating objects with predefined properties and behaviors.
Example:
class Car {
String model;
String color;
int year;
// Constructor
Car(String model, String color, int year) {
this.model = model;
this.color = color;
this.year = year;
}
// Method
void displayDetails() {
System.out.println("Model: " + model);
System.out.println("Color: " + color);
System.out.println("Year: " + year);
}
}
10. How do you define a constructor?
a) Same name as class
b) Must be static
c) Has return type
d) Uses void
Answer: Same name as class
Reason:
A constructor must have the same name as the class and no return type (not even
void).A constructor in Java is a special method used to initialize objects of a class. It has the same name as the class and does not have a return type, not even void. Constructors are automatically called when an object of the class is created using the new keyword. They are primarily used to set initial values for the object's attributes.
Example:
public class MyClass {
private int myNumber;
private String myString;
public MyClass() { // This is the constructor
myNumber = 0;
myString = "Default";
}
}
Question - 6
1. What is a setter method used for?
a) Assign values
b) Retrieve values
c) Print
d) Compile
Answer: Assign values
Reason:
A setter method sets (assigns) a value to a private variable of a class
Example:
class Student {
private int age;
public void setAge(int age) {
this.age = age;
}
}
2. How to create a final class?
a) final class ClassName()
b) class final ()
c) static final ()
d) class ClassName final
Answer: final class ClassName()
Reason: A final class cannot be extended (inherited).
Example:
final class ClassName { }
and
final class Animal {
// code
}
class Dog extends Animal { } // Error: Cannot inherit from final class
3. Which of these is not a Java data type?
a) int
b) double
c) real
d) boolean
Answer: real
Reason: Java has
int, double, boolean etc., but no "real" data type.Example:
int number = 10;
double price = 99.99;
boolean isAvailable = true;
4. What is the keyword to define a class variable?
a) static
b) final
c) private
d) constant
Answer: static
Reason: Static variables belong to the class, not to objects
In many programming languages like Java, the keyword "static" is used to define class variables. These variables belong to the class itself, not to any specific instance (object) of the class.
Example:
class Example {
static int count = 0;
}
or
public class MyClass {
// Class variable (static)
static int classVariable = 0;
// Instance variable
int instanceVariable = 0;
// Method to access the class variable
public static void incrementClassVariable() {
classVariable++;
}
}
5. How to make variable accessible in all classes?
a) public static
b) private
c) final
d) object variable
Answer: public static
Reason:
public makes it accessible anywhere, static makes it class-level.Meaning of public static:
-
public ➔ Anyone, anywhere in the program can use it.
-
static ➔ It belongs to the class, not individual objects. No need to create an object to access it.
Example:
public class Example {
public static int number = 10;
}
public class Example {
public static void main(String[] args) {
System.out.println(Example.number); // Output: 10
}
}
6. What is the output of: System.out.println("Hello"+100);?
a) Hello100
b) Error
c) Hello
d) 100Hello
Answer: Hello100
Reason:
"Hello" is a string, and 100 will be converted to string automatically and concatenated.Example:
Hello100
7. Can a method return an array?
a) Yes
b) No
c) Only object array
d) Only int
Answer: Yes
Reason: A method can return any array type (
int[], String[], etc.).Example:
public int[] getNumbers() {
return new int[] {1, 2, 3};
}
8. How to access array elements?
a) Index
b) Name
c) Class
d) Static
Answer: Index
Reason: Arrays are accessed by index starting from 0.
Example:
int[] numbers = {10, 20, 30};
System.out.println(numbers[1]); // Output: 20
9. What does method overriding mean?
a) Redefining inherited method
b) Duplicating method
c) Creating error
d) Calling constructor
Answer: Redefining inherited method
Reason: Child class redefines a method from the parent class with the same signature.
Example:
class Animal {
void sound() {
System.out.println("Animal makes sound");
}
}
class Dog extends Animal {
@Override
void sound() {
System.out.println("Dog barks");
}
}
10. Which keyword creates subclass?
a) extends
b) implements
c) class
d) super
Answer: extends
Reason:
extends keyword is used for inheritance (subclass creation)Example:
class Animal {
// code
}
class Dog extends Animal {
// Dog inherits Animal
}
Question - 7
1. Can we call non-static method from static?
a) No
b) Yes using object
c) Yes direct
d) Only in main
Answer: Yes using object
Reason:
Static methods belong to the class, not to any specific object.
Non-static methods belong to objects.
So, from a static method (like main), you cannot call a non-static method directly — you need to create an object first.
Example:
class Example {
void nonStaticMethod() {
System.out.println("Non-static method called");
}
static void staticMethod() {
Example obj = new Example();
obj.nonStaticMethod(); // Called using object
}
public static void main(String[] args) {
staticMethod();
}
}
2. How do we declare an ArrayList of Shing?
a) ArrayList <String> list = new ArrayList<>();
b) List <String> list = new ArayList<>();
c) Both a and b
d) Array <String> list
Answer: Both a and b
Reason:
1) Both ways are valid: using ArrayList directly or via the List interface.
2} ArrayList implements List.
Example:
import java.util.ArrayList;
import java.util.List;
class Example {
public static void main(String[] args) {
ArrayList<String> list1 = new ArrayList<>();
List<String> list2 = new ArrayList<>();
}
}
or
import java.util.ArrayList;
public class Main {
public static void main(String[] args) {
// Declare and initialize an ArrayList of Strings
ArrayList<String> names = new ArrayList<>();
// Add elements to the ArrayList
names.add("Alice");
names.add("Bob");
names.add("Charlie");
// Print the ArrayList
System.out.println(names);
}
}
3. What is the advantage of method overloading ?
a) Code readability
b) Speed
c) Data hiding
d) Security
Answer: Code readability
Reason:
Method overloading means having multiple methods with the same name but different parameters.
It makes the code clean and easy to understand.
Example:
class Calculator {
int add(int a, int b) {
return a + b;
}
double add(double a, double b) {
return a + b;
}
}
4. How to make variable accessible in all classes?
a) public static
b) private
c) final
d) object variable
Answer: public static
Reason:
public makes it accessible everywhere.
staticExample:
class A {
public static int number = 100;
}
class B {
public static void main(String[] args) {
System.out.println(A.number); // Accessing directly
}
}
5. How to create a final class?
a) final class ClassName{}
b) class final {}
c) static final {}
d) class ClassName final
Answer: final class ClassName{}
Reason:
final keyword before class prevents it from being inherited (no subclasses)Example:
final class Animal {
void sound() {
System.out.println("Animal Sound");
}
}
// class Dog extends Animal {} // ERROR: Cannot inherit from final class
7. How do you store multiple strings in jave?
a) Array of Strings
b) ArrayList
c) HashMap
d) All of these
Answer: All of these
Reason:
You can store multiple strings using:
-
Array of Strings
-
ArrayList
-
HashMap (key-value pairs, if you need mapping)
Example:
String[] array = {"Apple", "Banana", "Cherry"};
ArrayList<String> arrayList = new ArrayList<>();
arrayList.add("Apple");
arrayList.add("Banana");
HashMap<Integer, String> map = new HashMap<>();
map.put(1, "Apple");
map.put(2, "Banana");
8. What is a class in Java?
a) Blueprint
b) Object
c) Method
d) Variable
Answer: Blueprint
Reason:
A class is a blueprint for objects.
It defines properties and behaviors.
Example:
class Car {
String color;
void drive() {
System.out.println("Car is driving");
}
}
9. Which of the following allows multiple methods with the same name?
a) Method Overloading
b) Method Overriding
c) Inheritance
d) Encapsulation
Answer: Method Overloading
Reason:
Overloading = Same method name, different parameters.
Overriding = Same method in child class.
Example:
class Printer {
void print(String text) {
System.out.println(text);
}
void print(int number) {
System.out.println(number);
}
}
10. How do you access a static method?
a) Using object
b) Using class name
c) Using variable
d) Can't access
Answer: Using class name
Reason:
Static methods belong to the class, not an object.
You can call it directly using the class name.
Example:
class MathUtil {
static int add(int a, int b) {
return a + b;
}
}
class Test {
public static void main(String[] args) {
int result = MathUtil.add(5, 10); // Accessed using class name
System.out.println(result);
}
}
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