Constructor in java

What is Constructors?

A constructor is a special method in Java that is automatically executed when an object of a class is created. It is mainly used to initialize data members of a class.

Unlike normal methods, a constructor:

• It has the same name as the class.
• It does not have a return type.
• It is called automatically using the new keyword.

Why do we need Constructors?

Constructors are used because they:

• Initialize object data at the time of creation.
• Assign default or user-defined values.
• Ensure the object starts in a valid state.

Types of Constructors in Java

Default Constructor

• A constructor with no parameters is called a default constructor.

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

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

Parameterized Constructor

• A constructor that accepts parameters is called a parameterized constructor.

class Student
 {
    String name;
    int age;

    Student(String name, int age) 
    {
        this.name = name;
        this.age = age;
    }

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

Constructor Overloading

• When a class has multiple constructors with different parameters, it is called constructor overloading.

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

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

Rules of Constructors in Java

1. Constructor name must be the same as the class name.
2. Constructors do not have a return type.
3. Constructors can be overloaded.
4. Constructors cannot be inherited.
5. If no constructor is defined, Java provides a default constructor.

this Keyword in Constructors

• The this keyword refers to the current object of the class.
• It is commonly used when constructor parameters have the same name as instance variables.

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 acc1 = new Bank(101, "Kumar", 1000);
        Bank acc2 = new Bank(102, "Hari", 1500);

        System.out.println(acc1.accountNo);
        System.out.println(acc2.accountNo);
    }
}