Double.Nan question.plz help

[bnkiran kumar]

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
c is the answer, plz anyone answer.

[Edisandro Bessa]

Hi All,

I am getting prepared to write SCJP5 exam. Should I worry about Nan use for the exam or it's only for SCJP 1.4 ?

[mambe nanje]

well Double.NAN is not actually defined any where as a precise value, so any test about it will never be true

[Tilo Hemp]

interestingly,
Double.NaN != Double.NaN
gives true!

[marc weber]

Here's what I had in my own notes regarding NaN...

NaN is non-ordinal, so relational comparisons involving NaN always result in false. The only exception is NaN != NaN, which returns true. Wrapper methods Float.isNaN(float) and Double.isNaN(double) can be used to test for NaN. Alternatively, a float or double is NaN if it is not equal to itself (e.g., x != x).

Furthermore...

Math.round(Float.NaN) results in an int zero, and Math.round(Double.NaN) results in a long zero.

String literals "NaN" and "Infinity" are acceptable for Float and Double constructors.

float or double division by zero results in +/- Infinity; except dividing zero by zero, which results in NaN.

[Tilo Hemp]

Hi Marc,

thanks a lot for the interesting information!

I've got one remark and one question:

NaN is non-ordinal, so relational comparisons involving NaN always result in false. The only exception is NaN != NaN, which returns true.

--> the exception is not limited to NaN != NaN, but can also applied to say Double.NaN != 12.34, which also gives true. I guess != simply inverts the output of ==.

And my question is: what does "Cuius rei demonstrationem mirabilem sane detexi hanc marginis exiguitas non caperet." mean? I tried to find an automated latin-translator, but this did not work out

Regards

[marc weber]

Originally posted by Tilo Hemp:
...--> the exception is not limited to NaN != NaN, but can also applied to say Double.NaN != 12.34, which also gives true. I guess != simply inverts the output of ==...

You're correct! I guess it would be more accurate to say something like, "the exception is in applying the != comparison to NaN, which returns true -- even when comparing two NaNs."

As for the quote, see Fermat's Last Theorem (and note the enigmatic quality that made Fermat's words so intriguing in the first place ).

[Bert Bates]

And to answer an earlier question, this topic is on the 1.4 exam, but NOT the 1.5 exam.

[Tilo Hemp]

thanks a lot marc, this is quite funny!
especially, putting this quotation in a small margin under short and to-the-point statements

[bnkiran kumar]

marc weber ,thank you for your valuable material.