Constructors in Java

When creating an object in Java, we often want to initialize values at the time of object creation.

This is done using a constructor.

🔹 What Is a Constructor?

A constructor is a special method in Java that is automatically called when an object is created.

🔹 Key Points

• Constructor name is same as class name
• It does not have a return type
• Used to initialize objects
• Called using the new keyword

🔹 Why Do We Need a Constructor?

• To initialize data members
• To assign default values
• To ensure object is created in a valid state

🔹 Types of Constructors in Java

1️⃣ Default Constructor

A constructor with no parameters is called a default constructor.

class Student {
    Student() {
        System.out.println("Default constructor called");
    }
}

public class Main {
    public static void main(String[] args) {
        Student s = new Student();
    }
}

2️⃣ Parameterized Constructor

A constructor that accepts parameters is called a parameterized constructor.

class Student {
    String name;
    int age;

    Student(String n, int a) {
        name = n;
        age = a;
    }

    void display() {
        System.out.println(name + " " + age);
    }
}

🔹 Constructor Overloading

Having multiple constructors in the same class with different parameters is called constructor overloading.

class Student {
    Student() {
        System.out.println("Default");
    }

    Student(String name) {
        System.out.println("Name: " + name);
    }
}

🔹 Rules of Constructor

• Constructor name must match class name
• Constructors cannot be inherited
• Can be overloaded
• If no constructor is defined, Java provides a default constructor

🔹 this Keyword in Java

• The this keyword in Java is used to refer to the current object of a class.
• It is mainly used when instance variables and constructor parameters have the same name.

🔹 Why Do We Use this Keyword?

• To avoid confusion between instance variables and local variables
• To refer to the current object
• To call another constructor in the same class

🔹 Using this to Differentiate Variables
Example:

public class Bank {




        int accountNo;
        String name;
        int balance;

        Bank(int accountNo, String name , int balance)
        {
        this.accountNo = accountNo;
        this.name = name;
        this.balance = balance;
        }

        public static void main(String[] args)
        {

        Bank accholder = new Bank(101,"kumar",1000);
        System.out.println(accholder.accountNo);//101

        Bank accholder1 = new Bank(102,"hari",1000);
        System.out.println(accholder1.accountNo); //102


        }





    }