This week's book giveaway is in the Other Languages forum.We're giving away four copies of Functional Reactive Programming and have Stephen Blackheath and Anthony Jones on-line!See this thread for details.
Win a copy of Functional Reactive Programming this week in the Other Languages forum!

# Q'tion from Majji's paper

ashwini srinivasan
Greenhorn
Posts: 26

code//
The following code will print
1: Double a = new Double(Double.NaN);
2: Double b = new Double(Double.NaN);
3:
4: if( Double.NaN == Double.NaN )
5: System.out.println("True");
6: else
7: System.out.println("False");
8:
9: if( a.equals(b) )
10: System.out.println("True");
11: else
12: System.out.println("False");
A) True
True

B) True
False

C) False
True

D) False
False
The answer given is c) (False and True).
can anyone explain me how c) is the correct answer.
Thanx.

bill bozeman
Ranch Hand
Posts: 1070
From the API:

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:
If d1 and d2 both represent Double.NaN, then the equals method returns true, even though Double.NaN==Double.NaN has the value false.

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. This allows hashtables to operate properly.

So this is a special case. Also pay attention to 0.0 and -0.0 as this is the opposite of NaN.
Bill

ashwini srinivasan
Greenhorn
Posts: 26
Thanks a lot bill for nice explation.
regards
Ashwini.