Java Constructor

In Java, a constructor is a special type of method that is used to initialize objects. It is automatically called when an object of a class is created. Constructors help in setting initial values for object attributes.

Characteristics of a Constructor#

• A constructor has the same name as the class.
• It does not have a return type, not even void.
• It is automatically invoked when an object is created.
• Constructors can have parameters to initialize objects with different values.

Types of Constructors in Java#

1. Default Constructor#

A default constructor is a constructor without parameters. If no constructor is defined in a class, Java automatically provides a default constructor.

Example:#

// Defining a class
class Car {
    // Constructor
    Car() {
        System.out.println("Car object is created!");
    }

    public static void main(String[] args) {
        // Creating an object of Car class
        Car myCar = new Car();
    }
}

Output:#

Car object is created!

2. Parameterized Constructor#

A parameterized constructor allows us to pass values while creating an object.

Example:#

// Defining a class
class Car {
    String brand;
    int speed;

    // Parameterized Constructor
    Car(String b, int s) {
        brand = b;
        speed = s;
    }

    void display() {
        System.out.println("Brand: " + brand);
        System.out.println("Speed: " + speed + " km/h");
    }

    public static void main(String[] args) {
        // Creating objects with different values
        Car car1 = new Car("Tesla", 250);
        Car car2 = new Car("BMW", 220);

        // Displaying object details
        car1.display();
        car2.display();
    }
}

Output:#

Brand: Tesla
Speed: 250 km/h
Brand: BMW
Speed: 220 km/h

3. Copy Constructor#

A copy constructor creates a new object by copying the values of an existing object.

Example:#

class Car {
    String brand;
    int speed;

    // Parameterized Constructor
    Car(String b, int s) {
        brand = b;
        speed = s;
    }

    // Copy Constructor
    Car(Car obj) {
        brand = obj.brand;
        speed = obj.speed;
    }

    void display() {
        System.out.println("Brand: " + brand);
        System.out.println("Speed: " + speed + " km/h");
    }

    public static void main(String[] args) {
        Car car1 = new Car("Tesla", 250);
        Car car2 = new Car(car1); // Copying car1's values into car2

        car1.display();
        car2.display();
    }
}

Output:#

Brand: Tesla
Speed: 250 km/h
Brand: Tesla
Speed: 250 km/h

Constructor Overloading#

Constructor overloading allows a class to have multiple constructors with different parameters.

Example:#

class Car {
    String brand;
    int speed;

    // Default Constructor
    Car() {
        brand = "Unknown";
        speed = 0;
    }

    // Parameterized Constructor
    Car(String b, int s) {
        brand = b;
        speed = s;
    }

    void display() {
        System.out.println("Brand: " + brand);
        System.out.println("Speed: " + speed + " km/h");
    }

    public static void main(String[] args) {
        Car car1 = new Car(); // Calls default constructor
        Car car2 = new Car("Audi", 240); // Calls parameterized constructor

        car1.display();
        car2.display();
    }
}

Output:#

Brand: Unknown
Speed: 0 km/h
Brand: Audi
Speed: 240 km/h

Conclusion#

Constructors are essential in Java for initializing objects efficiently. We learned about:

• Default constructors (automatically created if no constructor is defined).
• Parameterized constructors (used to assign values while creating objects).
• Copy constructors (used to create a new object by copying values from another object).
• Constructor overloading (multiple constructors with different parameters).