How can "while (i == i) ;" be a non-infinite loop in a single threaded application?

Question

double i = Double.NaN;

The API for Double.equals() spells out the answer: "Double.NaN==Double.NaN has the value false". This is elaborated in the Java Language Specification under "Floating-Point Types, Formats, and Values":

NaN is unordered, so the numerical comparison operators <, <=, >, and >= return false if either or both operands are NaN. The equality operator == returns false if either operand is NaN, and the inequality operator != returns true if either operand is NaN. In particular, x!=x is true if and only if x is NaN, and (x<y) == !(x>=y) will be false if x or y is NaN.

The value of i is then Invalid. "Not a Number".

After some googling, i found out that you CAN have NaN ( Not a Number ) in Java! So, a Float Pointing number is the Data Type and the Value is NaN. See here

double i = Double.NaN;

NaN is not equal to anything, including itself.

float i = Float.NaN;
while(i == i) ;
System.out.println("Not infinite!");

Since others said it's NaN I got curious about the official (JDK 6) implementation of Double.isNaN, and behold:

/**
 * Returns <code>true</code> if the specified number is a
 * Not-a-Number (NaN) value, <code>false</code> otherwise.
 *
 * @param   v   the value to be tested.
 * @return  <code>true</code> if the value of the argument is NaN;
 *          <code>false</code> otherwise.
 */
static public boolean isNaN(double v) {
    return (v != v);
}

I'm not sure, but I believe (i == i) is not atomic operation in multithreaded process, so if i value will be changed by other thread between pushes of it's value to stack on thread executing the loop, then that condition can be false.