JAVA实现大数加法

转自：http://to-zoe-yang.iteye.com/blog/1097854

当计算非常大的数的相乘时，使用BigDecimal

便希望能自己实现大数的乘法
因为乘法里要使用加法，就先实现加法了
开始时，大数使用字符串保存
这时候我们需要将大数存储在一个数组里

为了节省空间，我们使用Byte存储每一位

ava代码  

 public static Byte[] StringToByte(String number){
     int len = number.length();
     Byte[] result = new Byte[len];
     //从高位到低位依次转换,转换后字符串"1234"变为4321,这样方便以后计算
     for(int i=0; i<number.length(); i++){
         byte curByte =  Integer.valueOf(number.charAt(i)+"").byteValue();
         result[len-i-1] = curByte;
     }

     return result;
 }

Java代码  

 public static Byte[] Add(Byte[] number1, Byte[] number2){
     int len = (number1.length>number2.length) ? number1.length : number2.length;
     Byte[] result = new Byte[len+1];
     Integer sum = new Integer(0);
     Integer carry = new Integer(0);
     int i;
     if(number1.length>number2.length){
         for(i=0; i<number2.length; i++){
             sum = number1[i].intValue() + number2[i].intValue();
             sum = sum +carry;
             carry = ((sum -10)>=0) ? 1:0;
             sum = ((sum -10)>=0) ? (sum-10):sum;
             result[i] = sum.byteValue();
             sum = 0;
         }
         for(;i<number1.length;i++){
             sum = sum +carry;
             carry = ((sum -10)>=0) ? 1:0;
             sum = ((sum -10)>=0) ? (sum-10):sum;
             result[i] = sum.byteValue();
             sum = 0;
         }
         if(carry!=0){
             result[i] = carry.byteValue();
         }else{
             result[i] = 0;
         }
     }else{
         for(i=0; i<number1.length; i++){
             sum = number1[i].intValue() + number2[i].intValue();
             sum = sum +carry;
             carry = ((sum -10)>=0) ? 1:0;
             sum = ((sum -10)>=0) ? (sum-10):sum;
             result[i] = sum.byteValue();
             sum = 0;
         }
         for(;i<number2.length;i++){
             sum = number2[i].intValue() + carry;
             carry = ((sum -10)>=0) ? 1:0;
             sum = ((sum -10)>=0) ? (sum-10):sum;
             result[i] = sum.byteValue();
             sum = 0;
         }
         if(carry!=0){
             result[i] = carry.byteValue();
         }else{
             result[i] = 0;
         }
     }

     return result;
 }