超级计算器——两个大数相乘

/**
* 超级计算器——两个大数相乘
*
* @author GaoHuanjie
*/
public class SuperCalculator {
public static void main(String[] args) {
String multiplier1 = "12";
String multiplier2 = "70";

//		String multiplier1 = "13286754398172596";
//		String multiplier2 = "2397567453241147";

System.out.println(multiplier1+"x" + multiplier2+"="+product(multiplier1, multiplier2));
}

/**
* 字符串顺序取反
*/
private static String reverse(String str) {
return new StringBuffer(str).reverse().toString();
}
/**
* 将char类型的数据转int类型
*/
private static int covertInt(char str){
return Integer.parseInt(String.valueOf(str));
}

public static String product(String multiplier1, String multiplier2) {//以12x70为例
char[] multiplierArray1 = reverse(multiplier1).toCharArray();// 高低位对调 {2,1}
char[] multiplierArray2 = reverse(multiplier2).toCharArray();// 高低位对调 {0,7}
int multiplierLength1 = multiplierArray1.length;// 2
int multiplierLength2 = multiplierArray2.length;// 2
int productSize = multiplierLength1 + multiplierLength2;//两个数的乘积的最大长度  4
int[] productArray = new int[productSize];//乘积数组 {0,0,0,0}
for (int j = 0; j < multiplierLength2; j++) {// 对齐逐位相乘  {0,7}
for (int i = 0; i < multiplierLength1; i++) {// {2,1}
productArray[i + j] = productArray[i + j] + (covertInt(multiplierArray1[i])* covertInt(multiplierArray2[j]));
}
}
//到此productArray元素为{0,14,7,0}

for (int i = 0; i < productSize; i++) {// 进位处理
//i=0 i=1  i=2 i=3
int quotient = productArray[i] / 10;//商   0   1    0   0
productArray[i] = productArray[i] % 10;//  0   4    8   0
if (quotient > 0) {
productArray[i + 1] = productArray[i + 1] + quotient;
}
}
//到此productArray元素为 {0,4,8,0}

int m = 0;
for (m = productSize - 1; m >= 0;) {// 找到最高位
if (productArray[m] > 0) {
break;
}
m--;
}
//至此m的值为 2

StringBuffer stringBuffer = new StringBuffer();
for (int n = 0; n <= m; n++) {// 由最高位开始打印乘积
stringBuffer.append(productArray[m - n]);
}
// 至此乘积为840
return stringBuffer.toString();
}
}