使用java BigInteger

大数加法 

import java.math.BigInteger;import java.util.Scanner;public class Nim {    public static void main(String[] args) {        Scanner cin=new Scanner(System.in);        BigInteger a=cin.nextBigInteger(),b=cin.nextBigInteger();        System.out.println(a.add(b));    }    }

大数乘法 

import java.math.BigInteger;import java.util.Scanner;public class Nim {	public static void main(String[] args) {		Scanner cin=new Scanner(System.in);		BigInteger a=cin.nextBigInteger(),b=cin.nextBigInteger();		System.out.println(a.multiply(b));	}	}