Double

[neel sri]

Double c = new Double(0.0);
Double d = new Double(-0.0);
System.out.println(c); //prints 0.0
System.out.println(d); // prints -0.0
System.out.println(c.equals(d)); //prints true

double d1 = 0.0 ;
double d2 =-0.0;
System.out.println(d1==d2); //prints flase
Can someone explain this.

Thankyou!!

[Tony Morris]

Floating-point types in Java follow IEEE754 standard.
http://www.xdweb.net/~dibblego/miscellaneous/documents/IEEE754.pdf

java.lang.Double follows its API Specification.
Here is an excerpt:

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 definition allows hash tables to operate properly.

Your assertion that the following code produces false is incorrect:

double d1 = 0.0 ; 
double d2 =-0.0;
System.out.println(d1==d2); //prints flase 

It prints true.
[ February 09, 2005: Message edited by: Tony Morris ]

[neel sri]

Sorry, My bad .. I meant this ..
System.out.println(c.equals(d)); //prints false
System.out.println(d1==d2); //prints true

Ended up writing asking the otherway..


anyways thanks for the reply, I got it now.