Large Numbers in Java

Question

How would i go about doing calculations with extremely large numbers in Java? i have tried long but that maxes out at 9223372036854775807, and when using an integer it does not save enough digits and therefore is not accurate enough for what i need. Is there anyway around this?

Answer 1

You can use the BigInteger class for integers and BigDecimal for numbers with decimal digits. Both classes are defined in java.math package.

Example:

BigInteger reallyBig = new BigInteger("1234567890123456890");
BigInteger notSoBig = new BigInteger("2743561234");
reallyBig = reallyBig.add(notSoBig);

Answer 2

Checkout BigDecimal and BigInteger.

Answer 3

Use the BigInteger class that is a part of the Java library.

http://java.sun.com/j2se/1.5.0/docs/api/java/math/BigInteger.html

Answer 4

Here is an example which gets big numbers very quickly.

import java.math.BigInteger;

/*
250000th fib # is: 36356117010939561826426 .... 10243516470957309231046875
Time to compute: 3.5 seconds.
1000000th fib # is: 1953282128707757731632 .... 93411568996526838242546875
Time to compute: 58.1 seconds.
*/
public class Main {
    public static void main(String... args) {
        int place = args.length > 0 ? Integer.parseInt(args[0]) : 250 * 1000;
        long start = System.nanoTime();
        BigInteger fibNumber = fib(place);
        long time = System.nanoTime() - start;

        System.out.println(place + "th fib # is: " + fibNumber);
        System.out.printf("Time to compute: %5.1f seconds.%n", time / 1.0e9);
    }

    private static BigInteger fib(int place) {
        BigInteger a = new BigInteger("0");
        BigInteger b = new BigInteger("1");
        while (place-- > 1) {
            BigInteger t = b;
            b = a.add(b);
            a = t;
        }
        return b;
    }
}

Answer 5

Depending on what you're doing you might like to take a look at GMP (gmplib.org) which is a high-performance multi-precision library. To use it in Java you need JNI wrappers around the binary library.

See some of the Alioth Shootout code for an example of using it instead of BigInteger to calculate Pi to an arbitrary number of digits.

http://shootout.alioth.debian.org/u32q/benchmark.php?test=pidigits&lang=java&id=3