What is a Constructor in Java?

A constructor in Java is a special method that is automatically called when an object is created.

It is used to initialize objects.

Key Features of Constructors

• Same name as the class
• No return type (not even void)
• Called automatically during object creation
• Can be overloaded (i.e., multiple constructors with different parameters)

Types of Constructors

1. Default Constructor (no parameters)
2. Parameterized Constructor (with parameters)
3. Constructor Overloading (multiple constructors)

Example 1: Default Constructor

class Car {
    // Default constructor
    Car() {
        System.out.println("Car object is created!");
    }
}

public class Main {
    public static void main(String[] args) {
        Car myCar = new Car(); // Constructor is automatically called
    }
}

Output:

Car object is created!

Example 2: Parameterized Constructor

class Student {
    String name;
    int age;

    // Parameterized constructor
    Student(String n, int a) {
        name = n;
        age = a;
    }

    void display() {
        System.out.println("Name: " + name + ", Age: " + age);
    }
}

public class Main {
    public static void main(String[] args) {
        Student s1 = new Student("Alice", 20);
        s1.display();
    }
}

Output:

Name: Alice, Age: 20

Example 3: Constructor Overloading

class Book {
    String title;
    int pages;

    // Constructor 1 - default
    Book() {
        title = "Unknown";
        pages = 0;
    }

    // Constructor 2 - parameterized
    Book(String t, int p) {
        title = t;
        pages = p;
    }

    void showDetails() {
        System.out.println("Title: " + title + ", Pages: " + pages);
    }
}

public class Main {
    public static void main(String[] args) {
        Book b1 = new Book();
        Book b2 = new Book("Java Basics", 250);

        b1.showDetails();
        b2.showDetails();
    }
}

Output:

Title: Unknown, Pages: 0  
Title: Java Basics, Pages: 250

Why Use Constructors?

• To initialize object fields when an object is created.
• To provide default or custom values.
• To keep code cleaner and more consistent.

Difference: Constructor vs Method