Java/Development Class/Big Integer
Содержание
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 http://www.davidflanagan.ru/javaexamples2.
*/
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
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(System.in));
// 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"))
break;
// 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.
table.add(BigInteger.valueOf(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));
table.add(nextfact);
}
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));
}
}
A trivial reverse-polish stack-based calculator for big numbers
import java.math.BigDecimal;
import java.util.Stack;
/** A trivial reverse-polish stack-based calculator for big numbers */
public class BigNumCalc {
/** an array of Objects, simulating user input */
public static Object[] testInput = {
new BigDecimal("3419229223372036854775807.23343"),
new BigDecimal("2.0"),
"*",
};
public static void main(String[] args) {
BigNumCalc calc = new BigNumCalc();
System.out.println(calc.calculate(testInput));
}
Stack s = new Stack();
public BigDecimal calculate(Object[] input) {
BigDecimal tmp;
for (int i = 0; i < input.length; i++) {
Object o = input[i];
if (o instanceof BigDecimal) {
s.push(o);
} else if (o instanceof String) {
switch (((String)o).charAt(0)) {
// + and * are commutative, order doesn"t matter
case "+":
s.push(((BigDecimal)s.pop()).add((BigDecimal)s.pop()));
break;
case "*":
s.push(((BigDecimal)s.pop()).multiply((BigDecimal)s.pop()));
break;
// - and /, order *does* matter
case "-":
tmp = (BigDecimal)s.pop();
s.push(((BigDecimal)s.pop()).subtract(tmp));
break;
case "/":
tmp = (BigDecimal)s.pop();
s.push(((BigDecimal)s.pop()).divide(tmp,
BigDecimal.ROUND_UP));
break;
default:
throw new IllegalStateException("Unknown OPERATOR popped");
}
} else {
throw new IllegalArgumentException("Syntax error in input");
}
}
return (BigDecimal)s.pop();
}
}
Big Integer demo
import java.math.BigInteger;
import java.util.ArrayList;
/*
* 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 http://www.davidflanagan.ru/javaexamples2.
*/
/**
* This program computes and displays the factorial of a number specified on the
* command line. It handles possible user input errors with try/catch.
*/
public class FactComputer {
public static void main(String[] args) {
// Try to compute a factorial.
// If something goes wrong, handle it in the catch clause below.
try {
int x = Integer.parseInt(args[0]);
System.out.println(x + "! = " + Factorial4.factorial(x));
}
// The user forgot to specify an argument.
// Thrown if args[0] is undefined.
catch (ArrayIndexOutOfBoundsException e) {
System.out.println("You must specify an argument");
System.out.println("Usage: java FactComputer <number>");
}
// The argument is not a number. Thrown by Integer.parseInt().
catch (NumberFormatException e) {
System.out.println("The argument you specify must be an integer");
}
// The argument is < 0. Thrown by Factorial4.factorial()
catch (IllegalArgumentException e) {
// Display the message sent by the factorial() method:
System.out.println("Bad argument: " + e.getMessage());
}
}
}
/**
* 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.
table.add(BigInteger.valueOf(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));
table.add(nextfact);
}
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));
}
}
Demonstrate large numbers
import java.math.*;
/**
* Demonstrate large numbers.
* @author Ian F. Darwin, http://www.darwinsys.ru/
* @version $Id: BigNums.java,v 1.4 2004/02/09 03:33:56 ian Exp $
*/
public class BigNums {
public static void main(String[] argv) {
//+
System.out.println("Here"s Long.MAX_VALUE: " + Long.MAX_VALUE);
BigInteger bInt = new BigInteger("3419229223372036854775807");
System.out.println("Here"s a bigger number: " + bInt);
System.out.println("Here it is as a double: " + bInt.doubleValue());
//-
}
}
