Another Big Integer : Big Integer « Development Class « Java

Another Big Integer

 * Copyright (c) 2000 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 2nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
 * You may study, use, and modify it for any non-commercial purpose.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book (recommended),
 * visit


import java.util.ArrayList;

import java.math.BigInteger;

 * This program displays factorials as the user enters values interactively
public class FactQuoter {
  public static void main(String[] args) throws IOException {
    // This is how we set things up to read lines of text from the user.
    BufferedReader in = new BufferedReader(new InputStreamReader(;
    // Loop forever
    for (;;) {
      // Display a prompt to the user
      System.out.print("FactQuoter> ");
      // Read a line from the user
      String line = in.readLine();
      // If we reach the end-of-file,
      // or if the user types "quit", then quit
      if ((line == null) || line.equals("quit"))
      // Try to parse the line, and compute and print the factorial
      try {
        int x = Integer.parseInt(line);
        System.out.println(x + "! = " + Factorial4.factorial(x));
      // If anything goes wrong, display a generic error message
      catch (Exception e) {
        System.out.println("Invalid Input");

 * This version of the program uses arbitrary precision integers, so it does not
 * have an upper-bound on the values it can compute. It uses an ArrayList object
 * to cache computed values instead of a fixed-size array. An ArrayList is like
 * an array, but can grow to any size. The factorial() method is declared
 * "synchronized" so that it can be safely used in multi-threaded programs. Look
 * up java.math.BigInteger and java.util.ArrayList while studying this class.
 * Prior to Java 1.2, use Vector instead of ArrayList

class Factorial4 {
  protected static ArrayList table = new ArrayList(); // create cache
  static { // Initialize the first element of the cache with !0 = 1.

  /** The factorial() method, using BigIntegers cached in a ArrayList */
  public static synchronized BigInteger factorial(int x) {
    if (x < 0)
      throw new IllegalArgumentException("x must be non-negative.");
    for (int size = table.size(); size <= x; size++) {
      BigInteger lastfact = (BigInteger) table.get(size - 1);
      BigInteger nextfact = lastfact.multiply(BigInteger.valueOf(size));
    return (BigInteger) table.get(x);

   * A simple main() method that we can use as a standalone test program for
   * our factorial() method.
  public static void main(String[] args) {
    for (int i = 0; i <= 50; i++)
      System.out.println(i + "! = " + factorial(i));


Related examples in the same category

1.Big Integer demo
2.A trivial reverse-polish stack-based calculator for big numbers
3.Demonstrate large numbersDemonstrate large numbers