The args[] array of a main() method is an array
of Strings.
Consider a class which counts the occurrences of the digits 0-9. For example you might wish to test the randomness of a random number generator. If a random number generator is truly random, all digits should occur with equal frequency over a sufficiently long period of time.
You will do this by creating an array of ten ints called ndigit. The zeroth component of ndigit will track the number of zeros; the first component will track the numbers of ones and so forth. The RandomTest
program below tests Java's random number generator to see if it produces apparently random numbers.
import java.util.Random;
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 < 10; i++) {
System.out.println(i+": " + ndigits[i]);
}
}
}
% javac RandomTest.java % java RandomTest 0: 10171 1: 9724 2: 9966 3: 10065 4: 9989 5: 10132 6: 10001 7: 10158 8: 9887 9: 9907 %There are three
for loops in this program, 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.