Simple java ID card 18th-digit algorithm

Public class identitynum {

Public static void main (string [] args ){
System. out. println (getlastidnum ("37018319880321312 "));
    }

/**
* Name: calculate the last digit of the 18-digit ID card.
* Function: calculate the last digit based on the ID number of the first 17 digits.
* Algorithm of the last digit of the ID card:
* 1. Multiply the first 17 digits of the ID card number by the weights: 7 9 10 5 8 4 2 1 6 3 7 9 10 5 8 4 2 2
* (For example, multiply the first digit by 7, the second digit by 9, and so on)
* 2. Then sum all the products above
* 3. Take the obtained mod and mod as 11 (% 11) and obtain a number smaller than 11 (0 to 11)
* 4. Then find the last digit from the first digit of the verification code: 1 0x9 8 7 6 5 4 3 2
* If 0 is obtained, the first digit is 1. If 1 is obtained, the second digit is 0.
* If the result is 2, it corresponds to the third digit: x. If the result is 3, it corresponds to the fourth digit: 9, and so on.
* 5. The last digit of the ID card is obtained.
*/
Public static character getlastidnum (string preids ){
Character lastid = null;
// When the input string does not contain 17 digits, it cannot be calculated and is directly returned.
If (preids = null & preids. length () <17 ){
Return null;
        }
Int [] weightarray = {,}; // Weight array
String vcode = "10x98765432"; // verification code string
Int sumnum = 0; // The first 17 is the number multiplied by the right and then the sum is obtained.
       
// Multiply the weights cyclically and then sum them.
For (int I = 0; I <17; I ++ ){
Int index = integer. parseint (preids. charat (I) + "");
Sumnum = sumnum + index * weightarray [I]; // multiply by the weight and then sum
        }
       
Int modnum = sumnum % 11; // modulo
Lastid = vcode. charat (modnum); // find the corresponding number from the verification code
       
Return lastid;
    }
}