Hello Jetto Net followers!

Welcome to our Java Object Oriented Programming (OOP) series. In the previous article, we learned that classes are templates of objects and objects are living instances of classes. In this article, we will examine “constructors”, an important concept that enables us to create objects.

What is a Constructor Method?

A constructor method is a special method that is called automatically when an object of a class is created. The main purpose of constructor methods is to set the initial state of the newly created object, that is, to give the properties (attributes) of the object their initial values. In this way, objects are ready for use as soon as they are created.

Properties of Constructor Methods

• Name: Constructor methods must have the same name as the class.
• Return Value: Constructor methods do not return any value. Therefore, void is not used as the return type.
• Access Specifiers: Constructor methods are usually defined as public, so that objects can be created from outside the class.
• Parameters: Constructor methods can take parameters to give the object's properties their initial values.

Default Constructor Method

If we do not define any constructor method for a class, the Java compiler automatically creates a constructor method with no parameters. This method is called the “default constructor method”. The default constructor method assigns default values to the properties of the object (0 for numeric types, false for boolean, null for objects).

public class Car {
   String brand
   String model
   int year
   String color;
   // Default constructor method (created automatically)
   /*
   public Car() {
       brand = null;
       model = null;
       year = 0;
       color = null;
   }
   */
}

Constructor Methods with Parameters

We can use parameterized constructor methods to give initial values to the object's properties in a more controlled way. Parametric constructor methods initialize the object's properties using the values given as parameters when the object is created.

public class Car {
   String brand
   String model
   int year
   String color;
   
   // Constructor method with parameters
   public Car(String brand, String model, int year, String color) {
       this.brand= brand;
       this.model = model;
       this.year= year;
       this.color= color;
   }
}

Copy Constructors

Copy constructor methods are used to create a copy of an existing object. These methods take an object of the same class as a parameter and copy its properties to the newly created object.

public class Car {
   String brand;
   String model;
   int year;
   String color;
   
   public Car(Car car) {
       this.brabd = car.brand;
       this.model = car.model;
       this.year = car.year;
       this.color= car.color;
   }
}

Use of Constructive Methods

Constructor methods are used with the new keyword. When the object is created, parameters are given to the constructor method.

Car myCar = new Car("BMW", "320i", 2023, "Blue");

In this example, we created an object named myCar from the Car class. While creating the object, we gave the values “BMW”, “320i”, 2023 and “Blue” to the parameterized constructor method. These values were used to initialize the brand, model, year and color properties of the object.

I hope this article has helped you understand the topic of constructor methods in Java. In the next installment, we will continue to explore other important concepts of OOP. If you have any questions, please let me know in the comments.

Happy coding!