import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.util.regex.Matcher; import java.util.regex.Pattern; /**  * 大数乘法的简单实现, 目前还不是很完善  * Fix:  * 1. 修改前后删除0的一些错误情况  * 2. 支持负数运算  * 3. 判断输入字符串是否符合小数定义, 用正则表达式判断  * @author icejoywoo  * @since 2012.2.16  * @version 0.1.1  */ public class BigNumber {     public static void main(String[] args) throws IOException {         System.out.println("Input two large integers:");         BufferedReader buffer = new BufferedReader(new InputStreamReader(System.in));         String[] strArray = buffer.readLine().split("\\*");         System.out.println(bigNumberMultiply(strArray[0], strArray[1]));     }     /**      * 计算两个任意大小和精度的数的乘积      * @param first 第一个参数      * @param second 第二个参数      * @return 两个数的乘积      */     private static String bigNumberMultiply(String first, String second) {         // 正负号判断标志         boolean flag = false;         if (first.charAt(0) == '-') {             flag = !flag;             first = first.substring(1);         }         if (second.charAt(0) == '-') {             flag = !flag;             second = second.substring(1);         }         // 小数点的位置         int aPoints = first.length() - first.indexOf('.') - 1;         int bPoints = second.length() - second.indexOf('.') - 1;         int pointPos = aPoints + bPoints; // 结果的小数点位置         // 删除小数点         StringBuffer aBuffer = new StringBuffer(first.replaceAll("\\.", ""));         StringBuffer bBuffer = new StringBuffer(second.replaceAll("\\.", ""));         int[] a = string2IntArray(aBuffer.toString());         int[] b = string2IntArray(bBuffer.toString());         int[] result = new int[a.length + b.length - 1]; // 保存结果的数组         // 计算         for (int i = 0; i < a.length; i++) {             for (int j = 0; j < b.length; j++) {                 result[i + j] += a[i] * b[j];             }         }         // result中的某一位大于9的话需要进位         for (int i = result.length - 1; i >= 0; --i) {             if (result[i] > 9) {                 result[i - 1] += result[i] / 10;                 result[i] = result[i] % 10;             }         }         StringBuffer buffer = new StringBuffer(); // 将result数组转换为字符串         for (int i = 0; i < result.length; ++i) {             // 添加小数点             if(result.length - i == pointPos) {                 buffer.append(".");             }             buffer.append(String.valueOf(result[i]));         }         if (buffer.indexOf(".") != -1)         {             // 删除最开始的0             int i = 0;             while (i < buffer.length()) {                 if (buffer.length() > 2 && buffer.charAt(i+1) == '.') { // 小数点前只有一个数 0.                     break;                 } else if (buffer.charAt(i) == '0') { // 删除最前边的0                     buffer.deleteCharAt(i);                     i = 0;                     continue;                 } else { // 当第一位不是0的时候                     break;                 }             }             // 删除末尾的0             i = buffer.length() - 1;             while (i >= 0) {                 if (buffer.length() > 2 && buffer.charAt(i-1) == '.') { // 小数点后直接是数字                     break;                 } else if (buffer.charAt(i) == '0') { // 删除末尾的0                     buffer.deleteCharAt(i);                     i = buffer.length() - 1;                     continue;                 } else { // 当最后一位不是0的时候                     break;                 }             }         }         // 根据符号位, 返回值的正负标志         if (flag) {             return "-" + buffer.toString();         } else {             return buffer.toString();         }     }     /**      * 将字符串装换为数组      * @param number      * @return      */     private static int[] string2IntArray(String number) {         // 判断输入是否符合浮点数的要求         Pattern pattern = Pattern.compile("^(-?\\d+|\\d*)\\.?\\d*$");         Matcher matcher = pattern.matcher(number);         if (!matcher.find()) {             throw new IllegalArgumentException("输入的数不正确!");         }         int[] result = new int[number.length()];         for (int i = 0; i < number.length(); i++) {             result[i] = (int) (number.charAt(i) - '0');         }         return result;     } }

Input two large integers: 1a*a22 Exception in thread "main" java.lang.IllegalArgumentException: 输入的数不正确! at BigNumber.string2IntArray(BigNumber.java:132) at BigNumber.bigNumberMultiply(BigNumber.java:54) at BigNumber.main(BigNumber.java:22)

Input two large integers: -23424.2300*02345.23400000 -54935300.61982

Python 2.6.5 >>> -23424.2300*02345.23400000 -54935300.619819999