Double wrapper class doubt?

[Joe San]

Hi guys,

The code below is also from Dan Chisholm,

class D {
  static boolean m(double v) {
    return(v != v == Double.isNaN(v)); //How to interpret this line??
  }
  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));
}}

Help me out guys with the commented line above?

[Barry Gaunt]

I'll start you off:

v != v == Double.isNaN(v)

Looking at the API for Double, I see that isNaN returns a boolean. So on the lefthand side of == must be a boolean. It can only be the result of v != v.

So we have:

(v != v) == Double.isNaN(v)    

Now you look at the Double API to see what the result of v != v is (where v is NaN). It's in the description of Double.NaN.

[Joe San]

Barry,

I knew that NaN is not equal to anything and when we say NaN == NaN returns false and NaN != anything will return true. My confusion was on how to group the operators like you showed by placing braces...

(v != v) == Double.isNaN(v)...

But still I want to know based on what rules we group the operators??

Thanks for the help.

[Satish Kota]

Originally posted by Jothi Shankar Kumar Sankararaj:
Barry,

I knew that NaN is not equal to anything and when we say NaN == NaN returns false and NaN != anything will return true. My confusion was on how to group the operators like you showed by placing braces...

(v != v) == Double.isNaN(v)...

But still I want to know based on what rules we group the operators??

Thanks for the help.

== and != operators have equal precedence. And for equal precedenct operators execution happens from left to right.

[Joe San]

Thanks for the help. So concluding, when there are two or more equal precedence operators in a statement, then the execution happens from left to right.

Thanks guys.

[Sanjeev Singh]

Satish Kota writes..
== and != operators have equal precedence. And for equal precedenct operators execution happens from left to right.

Satish,What about logical operators?

Jothi,Is this question is from mock for 1.4?Because I guess operator precedence is not a part of SCJP 5.0 exam.

[Joe San]

Sanjeev,

I'm aiming for 1.4 version. So the question is for 1.4 exam.

[Barry Gaunt]

Jothi, this is all very basic stuff. I get the impression you are not referring to any basic Java book where these topics are explained rather early on. Are you not, in fact, reading an introductory book on Java? (I do not refer to K & B because it expects its readers to have already learnt Java).

Anyway, operator precedence and association is very well presented on Roedy Green's Java Glossary Site

[Joe San]

Barry,

Thanks for the help.