是3749啊，下面是代码：提示说：Runtime Error

import java.util.Scanner;
public class Main{
public static void main(String[ ] args)
 { 
      System.out.println("START");
      String string1=caesar(); 
      System.out.println("END");
      System.out.println("START");
      String string2=caesar(); 
      System.out.println("END");
     System.out.println("START");
      String string3=caesar(); 
      System.out.println("END");
       System.out.println(string1);
       System.out.println(string2);
       System.out.println(string3);
 }
 public  static int searchIndex(char ch)
    {
    int i=0,k=0;
    char[] array={'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};
      while(i<26)
         {
           if(ch==array[i])
              {
               k=i;
               break; 
               }
           else
               i++;
         }
         return k;
     }
public static String caesar()
{
Scanner scan=new Scanner(System.in);
   String ciphertext=scan.nextLine();
   char[] array=ciphertext.toCharArray();
   char[] alphabet={'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};
   int index,j;
    for(j=0;j<array.length;j++)
     {
       if(!(array[j]>='A')&&(array[j]<='Z'))
          continue;
       else
         { 
           index=searchIndex(array[j]);
           index=index-5; 
           if(index>=26)
               index=index-26;
             if(index<0)
               index=index+26;
               array[j]=alphabet[index];           
          }
     }
     String str=new String(array);
     return str;
}
}
 到底怎么回事啊？、等待大牛的解答！谢谢诶