Why are constructors needed in java when we have methods..I see the advantage that we don't need to evoke it, but still why?desc

Question

And can you also tell me about "this"?

Answer 1

Constructors are needed to initialize objects

Answer 2

Here is whst I found related to constructors in java. Hope this helps to answer your question.

Following are the difference between constructor and method.

Constructor is used to initialize an object whereas method is used to exhibits functionality of an object.

Constructors are invoked implicitly whereas methods are invoked explicitly.

Constructor does not return any value where the method may/may not return a value.

In case constructor is not present, a default constructor is provided by java compiler. In the case of a method, no default method is provided.

Constructor should be of the same name as that of class. Method name should not be of the same name as that of class.

reference:
https://www.tutorialspoint.com/Difference-between-constructor-and-method-in-Java

Answer 3

no
s= Student(1,100) is assigning Student(1,100) to s
where as s.Student(1,100) is different

Answer 4

Good question Chaitanya mahaprabhu,

Think of a Box. If we talk about a box class then it will have some class variables (say length, breadth, and height). But when it comes to creating its object(i.e Box will now exist in computer’s memory), then can a box be there with no value defined for its dimensions. The answer is no.

So constructors are used to assign values to the class variables at the time of object creation, either explicitly done by the programmer or by Java itself (default constructor).

Answer 5

Test

Answer 6

BroFar I got it now... thank you!

Jayakrishna 😬 I am still not able to figure out why we need constructors when we can assign default value to variables using methods itself.... but I am sort of getting sense that constructors initiate some process before program proceeds forward....is that true?

Answer 7

Thank you for taking your time to answer @BroFar but when should we use it exactly?.....I am just confused with its purpose and usage

Answer 8

chaitanya mahaprabhu
Third para tells usage..
When you need to initialize some default values for an object data or properties, constructors are useful.

When start writing code, you understand it more clearly...!

Edit:

class Student{
public int id, marks;
Student()
{
this.id=0;
this.id=0;
}
Student(int Id, int marks)
{ this.id=Id;
this.marks=marks;
}
}
Student s=new Student();
System.out.println(s.id);
s=new Student(1,100);
System.out.println(s.id);
First constructor set default values. Second set input values... This way you can use it

Answer 9

Jayakrishna

class X
{
X(int a)
{
System.out.print(a);
}

void random(int b)
{
System.out.print(b);
}
}

When the function is called, won't it do the same thing as the constructor?.....I am sorry if I am being naive....I am just confused

Answer 10

chaitanya mahaprabhu
I already updated with an example above.
For your example...
You need to create object as
X obj=new X(2);
With this Contructor X(2) automatically gets executed and prints a vlaue...
But to call random function you need this statement
obj.random(2);

Answer 11

Jayakrishna
Umm..... soooo the only difference is the calling part?....to avoid the method call we can use constructor?....

And in your updated answer,
Is "s=Student(1,100)" same as s.Student(1,100)?

Answer 12

No you get error for calling like that...
See this same but different purpose constructor,

Student()
{
this.id=10;
this.id=100;
}
With privious
What differences you find in this..?
It setting 10,100 as default values..
You can set some output statements also for know a process started...
Edit:
Its S = new Student(1,100);
I missed new there..

Answer 13

But we can do that with method too right?

Answer 14

Sunny Akhil

Thank you for the answer!....

Answer 15

chaitanya mahaprabhu
In some scenarios, it's not recommended to use methods for assigning default values.
Ofcouse you can but for that you need first an object. You need to call that method through that object. It's about 2 steps that too consecutive. If order missed, result will be undefined behaviour.. In thread environment you can't predict which one executes first.. It's depends on processor availability. in that case results may weird without constructors usage.
Conbining those two steps, is we can say a Contructor.
Without object creation you can't call non-static methods.
[Ofcouse you can set default values by static variables but that sets 0 (for Integer) or null for strings. But you cant access null values.]

Simply its better to use constructors instead of methods for setting default values.. Objects creation allocates memory for object properties(data) on which any modification done by the methods.. Methods can't able to do that.
Java is object oriented programming , not functional programming..

Answer 16

Cont.
Everything is an object in java(almost). You can understand better if you know oops concepts and its advantages compare to other procedures.

These all in my understandings in my words. May be there others points which Iam missing. I hope this only give some way of understanding process or give you an idea how it works only...

Answer 17

Jayakrishna
I got it now....thanks a lot!!

Answer 18

chaitanya mahaprabhu
You're Wel come..