question about null object

[Anu Bhagat]

Hi,

It may sound stupid question, but I must ask
In the code below the object reference d2 is cerated using null d1. so what this object is like? is it also null?
also with line Dog d1 = null, do we get an object on the heap?

  

class Dog {
String name;
}
class DogTest{
Dog d1 = null;  //
Dogd2 = new Dog(d1);
 

Thanks in advance.

Anu

[Campbell Ritchie]

Have you tried it? Will that code actually compile?

[jittu goud]

Dog D2 = new Dog(d1);

you are using the non default Dog Constructor ..where is the implementaion of it ?

[David Newton]

@jittu goud: One way folks try to help beginners is to get them to think things through for themselves rather than just handing the answer to them!

[Anu Bhagat]

the complete code is like this

 
class Dog {
     String name;
     Dog d;
     Dog() { name = "Tuffy"; }
     Dog( Dog d) { this.d = d; }
}

public class DogTest {
    public static void main(String[] args) {
       Dog d1 = null;
       Dog d2 = new Dog(d1);
      }
}   

My question is- is d2 null? ( i think it should be - but not sure )do we get any object on heap? do null onject live on the heap?

[David Newton]

Why do you think it would be null? What, precisely, is happening when you execute the Dog(Dog d) constructor? Is is still instantiating a Dog?

[jittu goud]

David Newton wrote:@jittu goud: One way folks try to help beginners is to get them to think things through for themselves rather than just handing the answer to them!

oops my bad ....on the other side...iam a beginner myself..... :shock:

[jittu goud]

anu Its not null...

Dog d2 = new Dog(d1) ...

i think the "new Dog(d1)" will create a new object with null value
...but d2 will store the object reference ..rather than the actual object

in this case you should get the value of d2 as Dog@3e25a5

but still the d2.d will be null

[jittu goud]

 class Dog {  
        String name;
           Dog d; 
      Dog ()
      {
         this.name = "test";
         
      }
    
      Dog( Dog d) {
           this.d = d; 
      }  
   
public String toString() {
		return "name=" + name + " " + "Dog =" + d;
	}

   
       public static void main(String[] args) {  
        Dog d1 = null;  
        Dog d2 = new Dog(d1); 

        System.out.println(" D1 = "+d1);
        System.out.println(" by overriding tostring -->  "+d2);
       System.out.println(" D2 = "+d2.d);
 
       }
  
   }     

i made a few changes....to your code