Non viene trovato il main

[brouls]

Salve a tutti. Ho trovato questa classe su internet che mi servirebbe come base da cui partire. Volevo però prima provare a farla girare per vedere al dettaglio l'output, ma quando faccio per lanciarla ottengo questo errore : "Selection does not contain a main type"

Come mai? dove sta l'errore? Vi posto la classe :

import java.security.*;
   import javax.crypto.*;
   import javax.crypto.spec.*;
import java.io.*;

   /**
   * This program generates a AES key, retrieves its raw bytes, and
   * then reinstantiates a AES key from the key bytes.
   * The reinstantiated key is used to initialize a AES cipher for
   * encryption and decryption.
   */

   public class AES {

     /**
     * Turns array of bytes into string
     *
     * @param buf    Array of bytes to convert to hex string
     * @return    Generated hex string
     */
     public static void main(String[] args) throws Exception {

       String message="This is just an example";

       // Get the KeyGenerator

       KeyGenerator kgen = KeyGenerator.getInstance("AES");
       kgen.init(128); // 192 and 256 bits may not be available


       // Generate the secret key specs.
       SecretKey skey = kgen.generateKey();
       byte[] raw = skey.getEncoded();

       SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");


       // Instantiate the cipher

       Cipher cipher = Cipher.getInstance("AES");

       cipher.init(Cipher.ENCRYPT_MODE, skeySpec);

       byte[] encrypted =
         cipher.doFinal((args.length == 0 ?
          "This is just an example" : args[0]).getBytes());
       System.out.println("encrypted string: " + asHex(encrypted));

       cipher.init(Cipher.DECRYPT_MODE, skeySpec);
       byte[] original =
         cipher.doFinal(encrypted);
       String originalString = new String(original);
       System.out.println("Original string: " +
         originalString + " " + asHex(original));
     }
     
     public static String asHex (byte buf[]) {
         StringBuffer strbuf = new StringBuffer(buf.length * 2);
         int i;

         for (i = 0; i < buf.length; i++) {
          if (((int) buf[i] & 0xff) < 0x10)
           strbuf.append("0");

          strbuf.append(Long.toString((int) buf[i] & 0xff, 16));
         }

         return strbuf.toString();
        }

   } 

Grazie