Double.NaN (Majji Q)

[Cathy Song]

  
    class NaNEquals{
       public final static void main(String[] s)
      {
         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) )   //line2
            System.out.println("True");
         else
            System.out.println("False");
      }
   }

Output:
False
True
Can someone explain line 2? I always thought NaN was never equal to itself..
Thanks.

[Harwinder Bhatia]

Hi Cathy
The answer to this can be found in the Java API Reference for the 'equals' method of the Double class. Here's an excerpt:

Note that in most cases, for two instances of class Double, d1 and d2, the value of d1.equals(d2) is true if and only if
d1.doubleValue() == d2.doubleValue()
also has the value true. However, there are two exceptions:
1. If d1 and d2 both represent Double.NaN, then the equals method returns true, even though Double.NaN==Double.NaN has the value false.
2. If d1 represents +0.0 while d2 represents -0.0, or vice versa, the equal test has the value false, even though +0.0==-0.0 has the value true.

Cheers
Harwinder
[ November 14, 2003: Message edited by: Harwinder Bhatia ]

[Cathy Song]

Ahh I see..Thanks Harwinder.

[Mona Gadkari]

hi,
Cathy and Harwinder you both have great brains. I always read your questions and try to understand them. Hirwinder your explaination was impressing.
Mona(varijasmom)