why Float.NaN and Double.NaN?

[Prashant Neginahal]

Please have look on fallowing two lines,
float f=(float)Math.sqrt(-4);
System.out.println(f==Float.NaN);
Result is false.Then, what is the need of defining NaN fields in Float and Double wrapper classes.?
OR What is NaN..?
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Prashant

[Nayanjyoti Talukdar]

Hi,
In floating point comparison, if either operand is NaN, then the comparison is false.

[girish rateshwar]

hi,
All boolean operations involving "NaN" results in a false value.
Note:
Double.NaN > 1.0 -> false
Double.NaN < 1.0 -> false
Double.NaN == 1.0 -> false
Float.NaN < -3.0 -> false
Float.NaN > Float.POSITIVE_INFINITY -> false
Float.NaN < Float.POSITIVE_INFINITY -> false
(0.0 / 0.0) == (0.0 / 0.0) -> false
Regards,

[Nayanjyoti Talukdar]

Hi,
I think that's not for all boolean operations.
As for example...

Double d = new Double(Double.NaN);
Double d1 = new Double(Double.NaN);
d.equals(d1) -> true. Here also NaN is involved.
Regards
Nayan.

[girish rateshwar]

Hi,
Le me explain......
Consider this..
2 instances of class Double, d1 and d2.
The value of d1.equals(d2) is true if and only if
--->> d1.doubleValue() == d2.doubleValue() <<--
The result is true if and only if the argument is not null and is a Double object that represents a double that has the identical bit pattern to the bit pattern of the double represented by the object.
However, there are two exceptions:
--NOTE:*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.
And the above two exceptions clearly indicate as to y u r d1.equals(d2) returns TRUE.

Regards,


[ December 16, 2002: Message edited by: girish rateshwar ]
[ December 16, 2002: Message edited by: girish rateshwar ]

[Jim Yingst]

All boolean operations involving "NaN" results in a false value.
"Boolean operations" is too general here. The statement would be true for all equality and comparison operators (==, <, >, <=, >=) except for the != operator, which always returns true if either operand is NaN. There are also various methods (which might be considered "operations") such as equals() (already noted) and isNaN() which can return true. So be careful about generalizing like this...

[girish rateshwar]

Hi jim,
I guess the statement is way too abstract, sorry bout it.
Regards,