简单代码，使用java制作双色球功能

如何用java制作双色球程序？尽量简单一点，要给学生做参考


import java.util.Random;
import java.util.Scanner;
import java.util.ArrayList;
  
public class lottery
{
   private static ArrayList arr = new ArrayList(7);
   private static Random random = new Random();
   public static ArrayList arra()
   {
      int a = 0;
      int b = 0;
      int c = 1;
      int d = 0;
      b = random.nextInt(31) + 1;
      arr.add(b);
      while(a<6)
      {
         b = random.nextInt(31) + 1;
         a++;
         arr.add(b);
         d = arr.size();
         while(c < d)
         {
            if(b == (int)arr.get(c-1))
            {
               arr.remove(c-1);
               a--;
               break;
            }
            c += 1;
         }
         c = 1;
      }
      return arr;
   }
   public static void main(String[] args)
   {      
      ArrayList arr_new = new ArrayList(7);
      arr_new = arra();
      ArrayList arr_input = new ArrayList(7);
      int e = 0;
      int f = 0;
      while(e<7)
      {
         Scanner input = new Scanner(System.in);
         f = input.nextInt();
         arr_input.add(f);
         e = e + 1;
      }
      int money = 1;
      int g = 0;
      int h = 0;
      while(g<arr_new.size())
      {
         while(h<arr_input.size())
         {
            if((int)arr_new.get(g) == (int)arr_input.get(h))
            {
               money = money * 10;
            }
            h += 1;
         }
         h = 0;
         g += 1;
      }
      if(money == 1)
      {
         money = 0;
      }
      System.out.println("The total amount of money you won is " + money);
      System.out.println("The actual winning numbers are " + arr_new);
   }  
}

拿走不谢