Java Programming
Interview Questions with Answers

21. What is a method in Java?

Answer: A method in Java is a block of code that performs a specific task. It allows code reuse, improves readability, and supports modular programming.

• Methods are defined inside classes.
• They can take parameters and may return a value.

 Example

public void greet() {
    System.out.println("Hello, Java!");
}

22. How do you define and call a method in Java?

Answer: Defining a method:

return_type method_name(parameter_list) {
    // method body
}

 Example

public int add(int a, int b) {
    return a + b;
}

 Calling a method:

int result = add(5, 3);
System.out.println("Sum = " + result);

• If it’s a non-static method, use an object to call it.
• If it’s a static method, you can call it directly from the class.

23. What is method overloading?

Answer: Method overloading means defining multiple methods in the same class with the same name but different parameters (type, number, or order). It is a form of compile-time polymorphism.  Example

public void show(String name) {
    System.out.println("Name: " + name);
}
public void show(int age) {
    System.out.println("Age: " + age);
}

24. What is the difference between method overloading and overriding?

Answer:   Overriding Example

class Parent {
    void display() {
        System.out.println("Parent");
    }
}
class Child extends Parent {
    @Override
    void display() {
        System.out.println("Child");
    }
}

25. What is the use of return statement in a method?

Answer: The **return** statement is used to:

• Exit from the method.
• Send back a value to the calling method (if the method is not void).

 Example

public int square(int x) {
    return x * x;
}

If a method returns nothing, use return; or omit it in void methods.

26. What are method parameters and arguments?

Answer:  Example

// Parameter
public void greet(String name) {
    System.out.println("Hello, " + name);
}
// Argument
greet("Aman");

27. What is the difference between call by value and call by reference in Java?

Answer:  Example

void modify(int a) {
    a = a + 5;
}

Even after calling modify(x), the original x remains unchanged. For objects, the reference copy is passed, so object fields can be changed, but the reference itself can’t be reassigned.

28. What are default, static, and final methods?

Answer: Default Method:

• Introduced in Java 8, used inside interfaces.
• Can have a method body in an interface.

Example

interface A {
    default void show() {
        System.out.println("Default method");
    }
}

 Static Method:

• Belongs to the class, not the object.
• Can be called using the class name.

Example

class Test {
    static void display() {
        System.out.println("Static method");
    }
}
Test.display();

Final Method

• Cannot be overridden in subclasses.

Example

class A {
    final void show() {
        System.out.println("Final method");
    }
}

29. Can main() method be overloaded?

Answer: Yes, the main() method can be overloaded with different parameter lists. Only the standard version is used by JVM as the entry point:

public static void main(String[] args)

But you can create additional main() methods:

public static void main(String arg) {
    System.out.println("Overloaded main: " + arg);
}

You must call the overloaded version manually.

30. Can a method return multiple values in Java?

Answer: No, a method in Java cannot return multiple primitive values directly. But we can simulate returning multiple values using:

1. Array

public int[] getCoordinates() {
    return new int[]{10, 20};
}

2. Object (Best Practice)

class Result {
    int total;
    double average;
}

public Result calculate(int[] marks) { Result r = new Result(); r.total = …; r.average = …; return r; } 3. Collections

public Map<String, Object> getData() {
    Map<String, Object> map = new HashMap<>();
    map.put("name", "Aman");
    map.put("marks", 90);
    return map;
}

31. What is Object-Oriented Programming (OOP)?

Answer: Object-Oriented Programming (OOP) is a programming paradigm based on the concept of “objects”, which can contain data (fields) and methods (functions).  Key Principles of OOP:

1. Encapsulation – Wrapping data and methods into a single unit (class).
2. Inheritance – Acquiring properties from another class.
3. Polymorphism – One interface, many implementations.
4. Abstraction – Hiding internal details and showing only necessary features.

Java is a fully OOP-based language (except for primitive types).

32. What is a class and object in Java?

Answer: Class: A class is a blueprint/template for creating objects. It defines the data members and methods.

class Student {
    String name;
    int age;
    void display() {
        System.out.println(name + " is " + age + " years old.");
    }
}

 Object: An object is an instance of a class. It represents a real-world entity.

Student s1 = new Student(); // s1 is an object
s1.name = "Aman";
s1.age = 21;
s1.display();

33. What is encapsulation in Java?

Answer: Encapsulation is the process of binding data (variables) and code (methods) together in a single unit (class), and restricting access using access modifiers like private, public, etc.  Benefits:

• Data hiding
• Increased security
• Easier maintainability

 Example

class Employee {
    private int salary;
    public void setSalary(int s) {
        salary = s;
    }
    public int getSalary() {
        return salary;
    }
}

34. What is inheritance? Types of inheritance supported in Java?

Answer: Inheritance allows a class (child) to acquire properties and behaviors from another class (parent).   Syntax

class Parent {
    void show() { }
}
class Child extends Parent {
    void display() { }
}

 Types of Inheritance in Java:

1. Single – One subclass inherits one superclass.
2. Multilevel – A class inherits from a class that itself inherits another class.
3. Hierarchical – Multiple subclasses inherit a single superclass.
4. Multiple inheritance using classes is not supported (to avoid ambiguity) but can be achieved using interfaces.

35. What is the difference between super and this keyword?

Answer:

• this, Refers to the current class object
• super, Refers to the parent class object

  this usage, Example

class A {
    int x;
    A(int x) {
        this.x = x; // distinguish between local and instance variable
    }
}

 super usage, Example

class B extends A {
    B() {
        super(10); // call parent constructor
    }
}

36. What is constructor? What are its types?

Answer: A constructor is a special method that is automatically called when an object is created. Its name is same as the class and it has no return type.  Types of Constructors

1. Default Constructor – No parameters.
2. Parameterized Constructor – Takes arguments.
3. Copy Constructor (not built-in, but can be defined manually).

 Example class Car { String model; // Constructor Car(String m) { model = m; } }

37. What is constructor overloading?

Answer: Constructor overloading means having multiple constructors in the same class with different parameters.  Example

class Book {
    String title;
    int price;

// Constructor 1 Book() { title = “Unknown”; price = 0; } // Constructor 2 Book(String t, int p) { title = t; price = p; } } Java chooses the constructor based on the arguments provided.

38.What is a static block?

Answer: A static block is a block of code inside a class that is executed only once, when the class is loaded into memory.  Usage:

• Initialize static variables
• Load drivers/libraries

 Example

class App {
    static {
        System.out.println("Static block executed");
    }
    public static void main(String[] args) {
        System.out.println("Main method");
    }
}

 Output

Static block executed
Main method

39. What is polymorphism in Java?

Answer: Polymorphism means “many forms”. It allows objects to be treated as instances of their parent class rather than their actual class.  Types:

1. Compile-time Polymorphism (Method Overloading)
2. Runtime Polymorphism (Method Overriding)

 Example (Runtime)

class Animal {
    void sound() {
        System.out.println("Animal sound");
    }
}
class Dog extends Animal {
    void sound() {
        System.out.println("Dog barks");
    }
}
Animal obj = new Dog();
obj.sound(); // Output: Dog barks

40. What is the difference between abstraction and encapsulation?

Answer:  Example

• Abstraction hides unnecessary info:
  • ATM: You just press buttons (you don’t know internal code).
• Encapsulation hides data from outside:
  • Salary can’t be accessed directly – only via getSalary().