what actually constructor returns

[Nancy Antony]

Constructor does not allocate memory for the object/instance, that is done by new. what is the role of constructor is to initialize the instance variables. Now there are two issues which needs attention and I'd like to confirm with you ranchers

1. when I donot write any constructor in my class Java provides one, which we usually say that intializes the instance variables to their default values, but I think default construtor doesn't do anything as any variable screated on heap is automatically initialized, am I right?

2. What does constructor returns ? Current Object i.e this that means object reference as this is a reference to the current object. So I understand the process as such. new allocates memry and constructor is called by passing this to the constructor and the only code which is present in default constructor is return this and in paramterized constructor , return this statement is automatically added?

Any suggestions or additions....

[Prashant Shiralkar]

Nancy Antony wrote: when I donot write any constructor in my class Java provides one, which we usually say that intializes the instance variables to their default values

This no-arg constructor provided by Java does not initialize the instance variables to default values. The initialization happens even before this constructor is called.

but I think default construtor doesn't do anything as any variable screated on heap is automatically initialized, am I right?

Yes, that's correct.

What does constructor returns ? Current Object i.e this that means object reference as this is a reference to the current object. So I understand the process as such. new allocates memry and constructor is called by passing this to the constructor and the only code which is present in default constructor is return this and in paramterized constructor , return this statement is automatically added?

It's the new operator that calls the constructor and finally returns the reference to the new object. A constructor has no return type hence doesn't ever return anything.

[Ankit Garg]

Nancy Antony wrote:I think default construtor doesn't do anything as any variable screated on heap is automatically initialized, am I right?

Well not completely automatically. Objects in the heap too need to be assigned a value. While its right that the default constructor doesn't provide a value to the instance variables, they are provided a default value by the compiler at their declarations. So if I write this code

class MyClass {
   int i = 10;
   int j;
   String s;
}

Then after compilation this code would look something like this

class MyClass extends java.lang.Object{
   int i = 10;
   int j = 0;
   String s = null;
   MyClass() {
       super();
   }
}

[Javin Paul]

Hi Nancy,

Constructor can't return anything as it doesn't have any return type , what it ensures that super class gets initialized before sub class gets initilized by calling super() on first line.

Thanks
Javin

[Bharaathi Jagadisan]

why the constructor doesn't return any values

[Astha Sharma]

Ankit Garg wrote:

class MyClass {
   int i = 10;
   int j;
   String s;
}

Then after compilation this code would look something like this

class MyClass extends java.lang.Object{
   int i = 10;
   int j = 0;
   String s = null;
   MyClass() {
       super();
   }
}

Objects are formed at run time not at compile time. Then how can instance variables be initialized at compile time before instance of class is formed? Are they initialized at the time when class is loaded?

[Bharaathi Jagadisan]

Briefly explain about the constructor and why we are using it

[Joanne Neal]

Bharaathi Jagadisan wrote:Briefly explain about the constructor and why we are using it

This will explain the basics for you

[Jesper de Jong]

Bharaathi Jagadisan wrote:why the constructor doesn't return any values

A constructor is a special block of code that's called to initialize a new instance of a class. It doesn't need to return a value. Even if it were possible to return a value, then the Java language wouldn't have any syntax to get at this value.

The question is like asking why a cat can't ride a bicycle. It's because it's a cat, and cats just don't ride bicycles. Likewise, a constructor just doesn't return a value. That's just how it's defined in the Java programming language.

[Joanne Neal]

Jesper de Jong wrote:cats just don't ride bicycles

Not even on youtube ? They do just about everything else on there.

[Bharaathi Jagadisan]

thanks

[Aditya Jha]

Astha Sharma wrote:
Objects are formed at run time not at compile time. Then how can instance variables be initialized at compile time before instance of class is formed? Are they initialized at the time when class is loaded?

What Ankit meant to say was that if you write the code as

class MyClass {  
   int i = 10;  
   int j;  
   String s;  
}

then, the compiler (while compiling) "sees" or perceives it like

class MyClass extends java.lang.Object{  
   int i = 10;  
   int j = 0;  
   String s = null;  
   MyClass() {  
       super();  
   }  
}

[Astha Sharma]

ok...thanks