Java short note in constructor-Java programming

Constructor in java short note with example program

constructor

constructor is a method with the same name as the class name that is generally used to

Initialize the instance variable and does not return any value, not even void.

Before understanding what is constructor , let's see how object is created

Syntax of object creation

Classname objectname=new constructor();

here new  is java keyword  used to create an object (instance)

constructor are called automatically when a new object is created

when an object is created in java using the keyword new following things happen:

• Memory is allocated for new objects

• Instance variables of the objects are initialized, either to their initial values or to default values(0 for number,null for objects)

• A constructor is invoked

Constructor() is used to initialize the object

Rules to be followed creation of constructor

• constructor name must be equal to class names

• constructor does not have return type

It is  entirely different from a method but working is similar to the method

There are two types of constructor in java

1 Default constructor

2 Parameterized constructor

Example program in default constructor

class Student

{

String name;//here string is data type

int age;//int is another data type

public static void main(String args[])

{

Student std=new Student();

System.out.println(std.name);

System.out.println(std.age);

}

}

Output from CMD

Here string is null and integer is zero value given by java compiler

Because only variable declaration is done in the program

observe the program and its output

A constructor without any argument is called a default constructor

parameter constructor means we can  passing some inputs in the

object creation itself ,this type of constructor is called parameterized constructor

more notes in java

constructor overloading in java example program

static keyword in java