Why is this happening?

[Derek Mason]

I passed scjp exam long back but I still have a question!
How can this return true???
new Float(Float.NaN).equals(new FLoat(Float.NaN))
I thought comparison with NaNs always return false!
thanks.
Derek.

[Douggie Fox]

Derek,
It's because Double objects are immutable and as a result Java just puts 1 object into memory rather than 2. The comparison you're making is on object references not values.

HTH
Paul

[Derek Mason]

If that were the case:
System.out.println(new Float(Float.NaN)==new Float(Float.NaN));
Would print true but it does not!

[Denis Anoykin]

The object of Float class contains member with primitive type 'float'
Thus I think in case:
new Float(Float.NaN).equals(new FLoat(Float.NaN))
Java compares float primitives into the Float objects
And in this case:
System.out.println(new Float(Float.NaN)==new Float(Float.NaN));
Java compares refernces to Float objects. And there are different references.

[Thomas Paul]

When in doubt, check the API:
for f1.equals(f2)
If f1 and f2 both represent Float.NaN, then the equals method returns true, even though Float.NaN==Float.NaN has the value false.