Constructor &Types of constructor (with examples)

What is constructor ?

In Java, a constructor is a special method used to initialize objects. Unlike regular methods, constructors are invoked when an instance of a class is created. They have the same name as the class and do not have a return type. Constructors are essential for setting initial values for object attributes and preparing the object for use.

Why Do We Need Constructors in Java ?

Constructors play a very important role, it ensures that an object is properly initialized before use.

What happens when we don't use constructors:

Without constructors:

Objects might have undefined or default values.
Extra initialization methods would be required.
Risk of improper object state

When Java Constructor is Called?

Each time an object is created using a new() keyword, at least one constructor (it could be the default constructor) is invoked to assign initial values to the data members of the same class.

Types of Constructors in Java

Default Constructor (No-Argument Constructor)
Parameterized Constructor
Copy Constructor

1. Default Constructor in Java(No-Argument Constructor)

A constructor that has no parameters is known as default constructor. A default constructor is invisible. And if we write a constructor with no arguments, the compiler does not create a default constructor. Once you define a constructor (with or without parameters), the compiler no longer provides the default constructor. Defining a parameterized constructor does not automatically create a no-argument constructor, we must explicitly define if needed.

For example:

import java.io.*;

// Driver class
class Geeks{

    // Default Constructor
    Geeks() { 
        System.out.println("Default constructor"); 

    }

    // Driver function
    public static void main(String[] args)
    {
        Geeks hello = new Geeks();
    }
}

2. Parameterized Constructor in Java

A constructor that has parameters is known as parameterized constructor. If we want to initialize fields of the class with our own values, then use a parameterized constructor.

import java.io.*;

class Geeks {

    // data members of the class
    String name;
    int id;

    Geeks(String name, int id) {
        this.name = name;
        this.id = id;
    }
}

class GFG 
{
    public static void main(String[] args)
    {
        // This would invoke the parameterized constructor
        Geeks geek1 = new Geeks("Sweta", 68);
        System.out.println("GeekName: " + geek1.name
                           + " and GeekId: " + geek1.id);
    }
}

Copy constructor (TBD)

Reference:https://www.geeksforgeeks.org/java/constructors-in-java/
https://www.datacamp.com/doc/java/constructors

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Constructor &Types of constructor (with examples)

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