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

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
        byte curByte =  Integer.valueOf(number.charAt(i)+"").byteValue();
        result[len-i-1] = curByte;
    }

    return result;
}

	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

加法算法

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
            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
            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
            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
            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;
}