Java Constructors

• Constructor in Java
• Constructor Chaining in Java
• Constructor Overloading in Java
• Initializer Block in Java

Constructor in Java

A constructor in Java is a special method that is used to initialize objects. The constructor is called when an object of a class is created.

public class Car {
    String model;
    String color;

    // Constructor
    public Car(String model, String color) {
        this.model = model;
        this.color = color;
    }

    void displayDetails() {
        System.out.println("Model: " + model + ", Color: " + color);
    }

    public static void main(String[] args) {
        Car myCar = new Car("Tesla Model S", "Red");
        myCar.displayDetails();
    }
}

Constructor Chaining in Java

Constructor chaining is the process of calling one constructor from another constructor with respect to the current object.

public class Car {
    String model;
    String color;
    int year;

    // Constructor 1
    public Car(String model, String color) {
        this.model = model;
        this.color = color;
    }

    // Constructor 2
    public Car(String model, String color, int year) {
        this(model, color); // Calling constructor 1
        this.year = year;
    }

    void displayDetails() {
        System.out.println("Model: " + model + ", Color: " + color + ", Year: " + year);
    }

    public static void main(String[] args) {
        Car myCar = new Car("Tesla Model S", "Red", 2020);
        myCar.displayDetails();
    }
}

Constructor Overloading in Java

Constructor overloading is a technique in Java in which a class can have more than one constructor that differ in parameter lists.

public class Car {
    String model;
    String color;
    int year;

    // Constructor 1
    public Car(String model, String color) {
        this.model = model;
        this.color = color;
    }

    // Constructor 2
    public Car(String model, String color, int year) {
        this.model = model;
        this.color = color;
        this.year = year;
    }

    void displayDetails() {
        System.out.println("Model: " + model + ", Color: " + color + ", Year: " + year);
    }

    public static void main(String[] args) {
        Car myCar1 = new Car("Tesla Model S", "Red");
        Car myCar2 = new Car("Tesla Model 3", "Blue", 2021);
        myCar1.displayDetails();
        myCar2.displayDetails();
    }
}

Initializer Block in Java

Initializer blocks in Java are used to initialize instance variables. They run each time when an object of the class is created.

public class Car {
    String model;
    String color;
    int year;

    // Initializer block
    {
        year = 2020;
    }

    // Constructor
    public Car(String model, String color) {
        this.model = model;
        this.color = color;
    }

    void displayDetails() {
        System.out.println("Model: " + model + ", Color: " + color + ", Year: " + year);
    }

    public static void main(String[] args) {
        Car myCar = new Car("Tesla Model S", "Red");
        myCar.displayDetails();
    }
}