Below is the syntax highlighted version of Birthdays.java
from §1.4 Arrays.

/****************************************************************************** * Compilation: javac Birthdays.java * Execution: java Birthdays days trials * * Computes the number of people (by simulation) that must enter a room * until two of them share a birthday. Assumes birthdays are uniform * and independent from 0 to days-1. Repeats the experiment the specified * number of times and print the average. * prints the average * * % java Birthdays 365 100000 * Average = 24.65394 * * Remark: the expected number of people for days = 365 is about 24.61658. * (The median number is about 23, but the average is higher.) * ******************************************************************************/ public class Birthdays { public static void main(String[] args) { int days = Integer.parseInt(args[0]); // number of days int trials = Integer.parseInt(args[1]); // number of trials int people = 0; // total number of people over all trials // repeat trials times for (int t = 0; t < trials; t++) { // hasBirthday[d] = true if someone born on day d; false otherwise boolean[] hasBirthday = new boolean[days]; while (true) { people++; // one more person enters the room int d = (int) (days * Math.random()); // integer between 0 and days-1 if (hasBirthday[d]) break; // found two people with the same birthday hasBirthday[d] = true; // update array } } double average = (double) people / trials; System.out.println("Average = " + average); } }

Last updated: Tue Aug 30 09:58:33 EDT 2016.