if(0.0 == -0.0) - Sample question

[Ashish Soni]

All ,

I found a code mentioned below (http://www.examsguide.com/scjp/freequestions8.html)

if(0.0 == -0.0) {
System.out.println("true");
}
else{
System.out.println("false");
}

this prints true and my understanding is that 0 is neither negative nor positive.

Is there is any other reason also , Pleae explain.


Ashish

[vaibhav mishra]

what you understand explains the simple result
it is true because sign doesn't matter here

both sides of operator are equal and hence true is returned

[Henry Wong]

this prints true and my understanding is that 0 is neither negative nor positive.

This is not completely true. The IEEE floating point spec defines a positive zero and a negative zero. So, a zero can be positive or negative.

They are equal because the specification defines that a positive zero is equal to a negative zero.

But you can tell them apart... For example, the inverse of positive zero is infinity, while the inverse of negative zero is negative infinity.

Henry

[Henry Wong]

For an example of this, take a look at this code...

public static void main(String[] args) {
    System.out.println(1.0 / (0.0));
    System.out.println(1.0 / (-0.0));
}

As you can see, the negative sign attached to the zero is preserved, as the two answers are different.

Henry

[Ralph Jaus]

But note that corresponding wrappers are not equal:

Double d1 = 0.0; 
Double d2 = -0.0; 
System.out.println(d1 == d2); 
System.out.println(d1.equals(d2));     

will print false false.

[Madhukar Ojha]

Hi Ashish

This is one of two special cases .

+0.0 = -0.0 is true
Float.Nan = Float.Nan is false

It is specified in Java API.

[Saurabh Patil]

Originally posted by Henry Wong:
For an example of this, take a look at this code...

public static void main(String[] args) {
    System.out.println(1.0 / (0.0));
    System.out.println(1.0 / (-0.0));
}

As you can see, the negative sign attached to the zero is preserved, as the two answers are different.

Henry

Hi henry,

I coded that part with some of my own, and I got exiting results. My program was:

    
class example4 
{
public static void main(String[] args) 
{
System.out.println(56*0);
System.out.println("\n"+56*-0);
System.out.println("\n"+0/56);
System.out.println("\n"+0/-56);
 
System.out.println("\n"+1.0 / (0.0));    
System.out.println("\n"+1.0 / (-0.0));
}
}

The result printed was:
0
0
0
0
Infinity
-Infinity


Can anyone explain me why the 2nd and 4th zero was printed??

Regards,
Saurabh

[Henry Wong]

Can anyone explain me why the 2nd and 4th zero was printed??

The rules discussed in this topic applies to floating point numbers. Your example uses integers.

Henry
[ July 06, 2008: Message edited by: Henry Wong ]