Great! Let’s dive into Types of Constructors in Java with clear explanations and examples.

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Constructors in Java

• Definition: Special method used to initialize objects of a class.

• Key Points:

  1. Name same as the class.

  2. No return type (not even void).

  3. Called automatically when object is created.

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1. Default Constructor

• Definition: Constructor with no parameters.

• Types:

  • Compiler-provided default constructor: Automatically added if no constructor is defined.

  • User-defined default constructor: Explicitly written by the programmer.

Example (User-defined default constructor):

class Car {
    Car() { // Default constructor
        System.out.println("Car object created");
    }
}
public class Main {
    public static void main(String[] args) {
        Car c = new Car(); // Calls default constructor
    }
}

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2. Parameterized Constructor

• Definition: Constructor with parameters to initialize object with specific values.

Example:

class Car {
    String brand;
    int speed;

    Car(String brand, int speed) { // Parameterized constructor
        this.brand = brand;
        this.speed = speed;
    }

    void display() {
        System.out.println(brand + " " + speed);
    }
}
public class Main {
    public static void main(String[] args) {
        Car c1 = new Car("BMW", 200);
        c1.display(); // BMW 200
    }
}

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3. Copy Constructor (Manual in Java)

• Definition: Constructor that creates a new object as a copy of an existing object.

• Note: Java does not provide automatic copy constructors like C++, so we write manually.

Example:

class Car {
    String brand;
    int speed;

    Car(String brand, int speed) {
        this.brand = brand;
        this.speed = speed;
    }

    // Copy constructor
    Car(Car c) {
        this.brand = c.brand;
        this.speed = c.speed;
    }

    void display() {
        System.out.println(brand + " " + speed);
    }
}

public class Main {
    public static void main(String[] args) {
        Car c1 = new Car("Audi", 220);
        Car c2 = new Car(c1); // Copy constructor
        c2.display(); // Audi 220
    }
}

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4. Private Constructor

• Definition: Constructor declared private; used to restrict object creation outside the class.

• Use Case: Singleton pattern or utility classes.

Example (Singleton):

class Singleton {
    private static Singleton instance;

    private Singleton() {} // Private constructor

    public static Singleton getInstance() {
        if(instance == null) instance = new Singleton();
        return instance;
    }
}

public class Main {
    public static void main(String[] args) {
        Singleton s1 = Singleton.getInstance();
        Singleton s2 = Singleton.getInstance();
        System.out.println(s1 == s2); // true
    }
}

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✅ Summary Table – Types of Constructors