BigInteger和BigDecimal的用法见http://blog.csdn.net/ly50247/article/details/4361943 以下是关于大整数乘法的具体例子：
public class BigIntMutipli {
public static void main(String[] args) {
String s1 = new String("1234567898765432100000");
String s2 = new String("1234567899999999999999");
BigInteger bigA = new BigInteger(s1);
BigInteger bigB = new BigInteger(s2);
System.out.println(s1 + " x " + s2 + " = " + bigA.multiply(bigB));
String d1 = new String("12345678987654.321");
String d2 = new String("123456789999999.9999999");
BigDecimal deciA = new BigDecimal(d1);
BigDecimal deciB = new BigDecimal(d2);
System.out.println(s1 + " x " + s2 + " = " + deciA.multiply(deciB));
// 将BigInteger的数转为2进制 10代表十进制，2代表2进制
System.out.println(new java.math.BigInteger("123456", 10).toString(2));
}
}