about == equals

[krussi rong]

Hi,
here is the question:
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");

So why the answer is False
True.
if Double.NaN == Double.NaN is False,
How the a.equals(b) comes True.
and I really don't know why Double.NaN == Double.NaN if False. and what is NaN?
Thanks
Krussi

[Corey McGlone]

Check out the API Spec for Double. In particular, check out the description of the equals() method.
Corey