Wrappers

[anushree ari]

class D {
static boolean m(double v) {
return(v != v == Double.isNaN(v));
}
public static void main (String args[]) {
double d1 = Double.NaN;
double d2 = Double.POSITIVE_INFINITY;
double d3 = Double.MAX_VALUE;
System.out.print(m(d1) + "," + m(d2) + "," + m(d3));
}
}
the ans is true, true, true how?
how the exp are evualeted? the operators are same precedence.
thx

[Marilyn de Queiroz]

What happens if you put parens around it to force the precedence like:

  static boolean m( double v ) {
    return( v != ( v == Double.isNaN( v ) ) );
  }

??

[Bert Bates]

you are mixing apples and oranges here. this syntax (a == b == c) is NOT on the exam. separate your explorations of this weird syntax from your explorations of NaN , MAX_VALUE, etc.

[Yan Bai]

Originally posted by anushree ari:
class D {
static boolean m(double v) {
return(v != v == Double.isNaN(v));
}
public static void main (String args[]) {
double d1 = Double.NaN;
double d2 = Double.POSITIVE_INFINITY;
double d3 = Double.MAX_VALUE;
System.out.print(m(d1) + "," + m(d2) + "," + m(d3));
}
}
the ans is true, true, true how?

It will always get 'true' as the result, because when v != v == Double.isNaN(v) is evaluated, v!=v is evaluated first and returns 'false', false==Double.isNaN(v) of course returns 'true'.
Hope that helps.

[Keen Chen]

hi
scjp 1.4, that's u
but, i think, "v!=v is evaluated first and returns 'false'" ,error.
when v is a NaN,or infinite, v !=v always be true

[anushree ari]

thanks everybody,
but iam little bit confused about false==Double.isNan(v); how the result is true,
thx

[Jessica Sant]

Originally posted by anushree ari:

but iam little bit confused about false==Double.isNan(v); how the result is true,

assume Double.isNan(v) returns false
false == false --> is true

[Peter Tran]

Ok Let break it down:
When v is NaN
1. v != v is True because NaN when compare to any thing is alway false so !(false) = true
2. The only way for NaN compare to NaN is using the isNaN function so NaN(v) = true.
3. True == True so the m(v) = true
When v is infinity
v != v is Infinity == infinity so !infinity = false.
of course isNaN return false for any number not Nan so it is false.
false == false is true
When v is Double.MAX_VALUE it is the largest double value.
v != v again is false
isNaN(v) is also false
false == false is true

[anushree ari]

thx jessica, and peter,
now i got the result,
thx to everyone to replied my question