regarding constructor

[Gursewak Singh]

Hello everyone,

i have a question which is of no sense,but it is confusing me,
And Question is

As we can initialize a variable in class then why we use constructor.
As we know main purpose of constructor is to initialize a instance variables

[Ninad Kulkarni]

Whenever new object of a class created then constructor of class is executed.

[Gursewak Singh]

I know that Whenever new object of a class created then constructor of class is executed.
but what is need of it if we can initialize a instance variable without it?

as we know basically constructor are use to initialize a instance variable

[Gursewak Singh]

Mean to say i want to know more about the use of constructor

[Vijay Tidake]

Hi Gursewak,

As you already know that the constructor is used to initialize the variables.

Lets take the following example.

public class Vehicle {

	int noOfWheels=2;
	
	public Vehicle() {
        	
    }
	
    public Vehicle(int noOfWheels) {
    	this.noOfWheels=noOfWheels;
    	
    }
    
    public void drive(){
    	System.out.println("Im Driving "+noOfWheels+ "Wheeler");
    }
    
    public static void main(){
    	//By default the vehicle is 2 wheeler.
    	
    	Vehicle v=new Vehicle();
    	v.drive();
    	
    	//But now I want to drive 4 wheeler.For that we have to option
    	
    	//1. I need to write another class for 4 whealer.
    	
    	//2.Write the another method(Setter) to initialize the variable.
    	
    	
    	//But by using consructor(Overloaded) its very simple.I can use same class to drive any type of vehivle(2,4,8 etc)
    	
    	
    	Vehicle v=new Vehicle(4);
    	v.drive();
    	
    	
    }
    
    
}

So by means of constructor the things got simpler,to initialize the variable to appropriate state.


Hope that will help you.
Thanks

[Ninad Kulkarni]

@Gursewak
Go through Constructor Declarations and Initialization of Fields you will understand use of constructor.

You can initialize instance variable either in constructor or in instance initialization block, it may depends on requirement.

See the code given below

public class Test {
	{
		System.out.println("First Instance Block");
	}

	public Test() {
		System.out.println("Constructor");
	}
	{
		System.out.println("Second Instance Block");
	}
	public static void main(String[] args) {
		new Test();
	}
}

Output of above code is given below
First Instance Block
Second Instance Block
Constructor


While creating an instance after instance initialization block constructor will execute.

I hope this may help you.

[himanshu jaggi]

Constructors are used to initialize the objects only once as soon as a new object is created by using new keyword.
constructors must have its name same as class name and also only placed after new keyword.
constructors are called only once so that no other method can call it.


Better example:- doctors(constructors) use to give all the necessary vaccinations to a newly born child(object) only once.

[Henry Wong]

Gursewak Singh wrote:
but what is need of it if we can initialize a instance variable without it?

as we know basically constructor are use to initialize a instance variable

I am assuming that you are just learning Java -- or even just learning object oriented programming. At this point in your training, objects are probably nothing more than just data structures; and class definitions are probably just a bit of business logic with some instance variables.

As your training continues, constructing an object may include very complex initialization processes. These processes may construct tons of other objects, access databases, access messaging systems, make tons of calls to services, and have tons of combinations to construct your class instances. In that regard, it will probably be much more clearer to why you should provide constructors, than expect your users to configure everything correctly for your instance.

Henry

[Gursewak Singh]

Ok,
Thank you Henry,Himanshu,Ninad And Vijay.

now i have better idea about constructors

thank you very much.....