Understanding the Constructor and Default Constructor

In this lesson, we will learn about the constructor and then about the default constructor.

What is a Constructor?

In Java, a constructor is a special method invoked when an object is created.

• Characteristics:
  • Has the same name as the class.
  • Does not have a return type.

Syntax of a Constructor

class ClassName {
    // constructor
    ClassName() {
        // Initialization code (optional)
    }
}

Explanation:

• ClassName(): The constructor method with the same name as the class and no parameters.
• Initialization code (optional): Code inside the constructor can initialize member variables or perform other setup tasks. This part is optional; if omitted, member variables receive their default values.

Explanation:

• Car(): Here, we have written a no-argument constructor for the Car class.
• brand = "Unknown";, color = "Unpainted";, year = 0;: These lines assign default values to the class member variables brand, color, and year respectively.
• Car myCar = new Car();: This line creates a new Car object named myCar using this no-argument constructor.
• myCar.displayDetails();: Calls the displayDetails method to print the initialized values of myCar.

Now, let's understand the default constructor.

What is a Default Constructor?

A default constructor is an automatically provided constructor by the Java compiler if no constructors are defined in the class. It initializes object variables with default or specified values.

Example: Animal Class with Default Constructor

This example demonstrates a default constructor in the Animal class.