I am sorry that I was out of town for a few days.

There is finite number of memory storage so there is no way to represent infinite number of all values.
For "double" defined in java/ejs, it use 8 byte to represent a number.
And the maximum number can be represented is about 10[sup]138[/sup] , there is no way to stored infinite number of different values.
The maximum value is defined as Double.POSITIVE_INFINITY / Doublle.NEGATIVE_INFINITY

For real world problem, if the distance is 100 or 1000. times larger than focus length, it can almost be treated as infinity (the error is too small to be neglected).