NAN Question,Please help.

[WiLL Tao]

 class  MyCheck
{
public static void main(String[] args) 
{
MyCheck c = new MyCheck();
c.check();
}
 public void check() 
 { 
 Double a = new Double(Double.NaN); 
 Double b = new Double(Double.NaN); 
 
 if( Double.NaN == Double.NaN ) 
 System.out.println("True"); 
 else 
 System.out.println("False"); 
 
 if( a.equals(b) ) 
 System.out.println("True"); 
 else 
 System.out.println("False"); 
 } 
}
 

when i ran code, got False,Ture;don't know why,anyone can explain it?TIA

[Rob Ross]

This question really has nothing to do with NaN. It's about object equivalence.
Two different objects (like your Double objects) can NEVER be equivalent, ie, the same object, because they are different objects.
Object ob1 = new Object();
Object ob2 = new Object();
ob1 and ob2 are two different Objects, so this code will always evaluate to false:
ob1 == ob2.
This is the same situation you have with comparing your doubles. You have

Double a = new Double(Double.NaN);  Double b = new Double(Double.NaN);  

'a' and 'b' are two different objects, so they can NEVER return true when you write
a == b.
[ April 17, 2002: Message edited by: Rob Ross ]

[Ricardo Cortes]

Hi Will...
a and b have the same value but do not reference the same object. thus, that is why you see the results you see.

[WiLL Tao]

I got it.
Thank you. Rob and Ricardo.

[Junilu Lacar]

Refer to the JLS �4.2.3 and �4.2.4 to see why
Double.NaN == Double.NaN
is false.
Also, see the JavaDocs for java.lang.Double to see why
a.equals(b)
is true.
Junilu

[Joshua Kueck]

Maybe Im missing something.. but where does the code have a==b?
I see Double.NAN.. but that has nothing to do with either object a or b..
I see a.equals(b).. but again.. no a==b
Just remember that if f1 and f2 are NaN, then f1.equals(f2) returns true, and that Float.NaN==Float.NaN returns false.
This is the opposite of: if f1 is 0.0f and f2 is -0.0f, then f1.equals(f2) is false and that 0.0f==-0.0f is true.

[Marilyn de Queiroz]

Originally posted by Joshua Kueck:
Maybe Im missing something.. but where does the code have a==b?

Inside the code tags of Rob's example in his reply.

[Rob Ross]

Joshua is right, my bad. I must have been half-asleep. I saw the Double, and the ==, and thought he was trying to compare two objects , but in reality he's comparing two floating point literals that are NaN.
Sorry.
Move along.
Nothing to see here
:roll: