See nfc()

Two things:
1. To make sure you work with doubles add a letter d behind the number.
2. Doubles aren't accepted everywhere in Processing 1.5.1, so you have to do the formatting manually.

Code Example

1. void setup() {
2.   size(800, 400);
3.   background(0);
4.   double number = 1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000d;
5.   text(df(number), 50, height/2);
6. }
7.  
8. String df(double number) {
9.   NumberFormat nf = NumberFormat.getInstance();
10.   return nf.format(number);
11. }

I ended up just writing my own large number class.

Hello All,

For the first question, just add  import java.text.*; to the begining of the code. 2.0 does not import all the stuff 1.5.1 did. NumberFormat is a plain java class.

And indeed, Processing doesn't work with doubles, so its functions doesn't accept them.

Lot of people stumble upon this error, enough to warrant it is a FAQ...
So I made a new entry:
http://wiki.processing.org/w/Cannot_find_a_class_or_type_named_%22Xxx%22

Of course, this supposes people think about searching the error on the Processing site... But it allows to just paste the link to this page as an answer, too... (that's the main reason for starting this Technical FAQ!).