线程“ main”中的异常

Question

Hello when I'm trying to run this code I'm getting following error I understand this happens when there is no main function, however I do have a main fuction..

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
at FilterAs.main(FilterAs.java:21)

Here's my code

  import java.io.*;
public class FilterAs {
public static int numberOfFiles(File directory) {  
      if (directory.isFile())  
         return(1);  
      else {  
         File[] list = directory.listFiles();  

         int count = 0;  

         if (list != null)  
            for (File file : list)  
               count += (file.isFile()) ? 1 : numberOfFiles(file);  

         return(count);  
      }  
   }  

   public static void main(String[] args) {  
      System.out.println(numberOfFiles(new File(args[0])));  
   }  

}  

Answer 1

I guess you forgot to set arguments for your program?

You are accesing the arguments when calling the method (numberOfFiles).

Answer 2

If there are no command line arguments passed to the program, the following would throw ArrayIndexOutOfBoundsException since the args array would be empty.

System.out.println(numberOfFiles(new File(args[0])));  

You should check for the existence of such arguments before accessing the args array :

if (args.length > 0) {
    System.out.println(numberOfFiles(new File(args[0])));  
} else {
    System.out.println("Please supply a file name"); 
}

Answer 3

You have a call to:

args[0]

But args is empty.

You have called your program with something like:

java -jar MyJar.jar

But you should have called it with:

java -jar MyJar.jar /a/path/to/some/directory

ie you need to pass an argument to your application.