步驟：1. 兩位年份填充為四位；2. 生成最後一位校驗位；

程式碼如下：

package com.mingo.common;

import java.util.Scanner;

public class IDcard15bitTo18bit {

    public static String[] trans15bitTo18bit(String[] input){
        String[] result = new String[18];
        for(int i=0;i<input.length;i++){
            if(i<=5){
                result[i] = input[i];
            }else
 
{
                result[i+2] = input[i];
            }
        }
        //年份最後兩位小於17,年份為20XX，否則為19XX
        if(Integer.valueOf(input[6])<=1&&Integer.valueOf(input[7])<=7){
            result[6]="2";
            result[7]="0";
        }else{
            result[6]="1";
            result[7
 
]="9";
        }
        //計算最後一位
        String[] xs = {"7","9","10","5","8","4","2","1","6","3","7","9","10","5","8","4","2"};
        //前十七位乘以係數[7,9,10,5,8,4,2,1,6,3,7,9,10,5,8,4,2],
        int sum = 0;
        for(int i=0;i<17;i++){
            sum+= Integer.valueOf(result[i]) * Integer.valueOf(xs[i]);
        }
        //對11求餘，的餘數 0 - 10 
 

        int rod = sum % 11;
        //所得餘數對映到對應數字即可
        if(rod==0){ result[17] = "1";
        }else if(rod==1){ result[17] = "0";
        }else if(rod==2){ result[17] = "X";
        }else if(rod==3){ result[17] = "9";
        }else if(rod==4){ result[17] = "8";
        }else if(rod==5){ result[17] = "7";
        }else if(rod==6){ result[17] = "6";
        }else if(rod==7){ result[17] = "5";
        }else if(rod==8){ result[17] = "4";
        }else if(rod==9){ result[17] = "3";
        }else if(rod==10){ result[17] = "2";}

        return result;
    }
    public static void main(String[] args) {
         //建立輸入物件
         Scanner sc=new Scanner(System.in);
         //獲取使用者輸入的字串
         String str="";
         System.out.print("請輸入您的15位身份證號：");
         str=sc.nextLine();
         System.out.println("您輸入的15位身份證號為："+str);
         if(str.length()==15){
             String[] input = str.split("");
             String[] result = trans15bitTo18bit(input);
             System.out.print("您的18位身份證號是：");
             for(String c:result){
                 System.out.print(c);
             }
         }else{
             System.out.println("不符合格式的身份證號！");
         }
    }

}