Computing Fibonacci numbers import java.io.*; import java.math.BigInteger; /** * BigFib is a simple class for computing Fibonacci * numbers, using the Java multi-precision integer * class java.math.BigInteger. */ public class BigFib { BigInteger last; BigInteger next; int n; /** * Create a new BigFib object, initialized to 0 on * the Fibonnacci sequence. */ public BigFib () { n = 0; last = new BigInteger("0"); next = new BigInteger("1"); } /** * Compute c more Fibonnacci numbers, returning the * last one. Ideally, c should be even and >0. * If you want to print the numbers too, pass printTo * as non-null. */ public BigInteger getFib(int c, PrintStream printTo) { BigInteger tmp; for( ; c > 0; c -= 2) { last = last.add(next); n++; if (printTo != null) printTo.println(" " + n + "\t" + last); next = next.add(last); n++; if (printTo != null) printTo.println(" " + n + "\t" + next); } if (c == 0) return next; else return last; } /** * Default limit for self-test. */ public static final int defaultLimit = 100; /** * Self-test code, accepts an integer from the * command line, or uses the default limit. */ public static void main(String args[]) { BigInteger answer; BigFib fib = new BigFib(); System.out.println("\t\t Fibonacci sequence!"); System.out.println(""); System.out.println(); int limit = 100; if (args.length > 0) { try { limit = Integer.parseInt(args[0]); } catch (NumberFormatException nfe) { System.err.println("Bad number, using default " + limit); } if (limit < 1) { limit = defaultLimit; System.err.println("Limit too low, using default " + limit); } } answer = fib.getFib(limit, System.out); } }