java里如果只有一个类，而且是public时有什么命名规则之类么，新人求教

在我编译器上这个代码完全正确，但是在pat在线编程上就报错
package a;
import java.util.Scanner;

public class A
{
    public static void main(String[] args)//12345 15 one five
    {
        Scanner in=new Scanner(System.in);
        String a=in.nextLine();   
        String b;
        int sum=0;
        for(int i=0;i<a.length();i++)            
        { sum+=a.charAt(i)-'0';}
        b=String.valueOf(sum);
        for(int i=0;i<b.length();i++)
        { if(i==b.length())
        {
            switch(b.charAt(i))
            { case '0':System.out.printf("zero");break;
            case '1':System.out.printf("one");break;
            case '2':System.out.printf("two");break;
            case '3':System.out.printf("three");break;
            case '4':System.out.printf("four");break;
            case '5':System.out.printf("five");break;
            case '6':System.out.printf("six");break;
            case '7':System.out.printf("seven");break;
            case '9':System.out.printf("nine");break;
            case '8':System.out.printf("eight");break;
            }}
            else
            {
            switch(b.charAt(i))
            { case '0':System.out.printf("zero ");break;
            case '1':System.out.printf("one ");break;
            case '2':System.out.printf("two ");break;
            case '3':System.out.printf("three ");break;
            case '4':System.out.printf("four ");break;
            case '5':System.out.printf("five ");break;
            case '6':System.out.printf("six ");break;
            case '7':System.out.printf("seven ");break;
            case '9':System.out.printf("nine ");break;
            case '8':System.out.printf("eight ");break;
            }}
        }
        //System.out.println()
        in.close();
    }
   

}