As our second example let's consider a class that counts the occurrences of the digits 0-9 in decimal expansion of the number pi, for example. This is an issue of some interest both to pure number theorists and to theologians

We will do this by creating an array of ten longs called ndigit . The zeroth element of ndigit will track the number of zeroes in the input stream; the first element of ndigit will track the numbers of 1's and so on. We'll test Java's random number generator and see if it produces apparently random numbers.

import java.util.*; class RandomTest { public static void main (String args[]) { int[] ndigits = new int[10]; double x; int n; Random myRandom = new Random(); // Initialize the array for (int i = 0; i < 10; i++) { ndigits[i] = 0; } // Test the random number generator a whole lot for (long i=0; i < 100000; i++) { // generate a new random number between 0 and 9 x = myRandom.nextDouble() * 10.0; n = (int) x; //count the digits in the random number ndigits[n]++; } // Print the results for (int i = 0; i <= 9; i++) { System.out.println(i+: + ndigits[i]); } } } We've got three for loops in this code, one to initialize the array, one to perform the desired calculation, and a final one to print out the results. This is quite common in code that uses arrays.