How can solve this problem in credit card ,i'm beginner in java

Exception in thread "main" java.lang.NumberFormatException: For input string: "2315778 "
	at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
	at java.lang.Integer.parseInt(Integer.java:492)
	at java.lang.Integer.parseInt(Integer.java:527)
	at javaapplication1.JavaApplication1.checkDigits(JavaApplication1.java:54)
	at javaapplication1.JavaApplication1.main(JavaApplication1.java:18)
Java Result: 1

public class JavaApplication1
{
   /**
    * @param args the command line arguments
    */
   public static void main(String[] args)
   {
      int num = 2315778;
      System.out.println("Credit card number: " + num + " is " + checkDigits(num));
      num = 1234567;
      System.out.println("Credit card number: " + num + " is " + checkDigits(num));
      num = 7654321;
      System.out.println("Credit card number: " + num + " is " + checkDigits(num));
      num = 1111111;
      System.out.println("Credit card number: " + num + " is " + checkDigits(num));
   }

   public static int decode(int digit, boolean even)
   {
      int a = 0;
      if (even )
      {
          a = digit * 2;
          if ( a >9)
          {
             a = (a+1) % 10;
          }
          return a;
      }
      else
      {
         return digit;
      }
   }

   public static String checkDigits(int cardNo)
   {
      String a = new String ();
      a = cardNo + " ";
      char [ ] array = a.toCharArray ( );
      int [ ] array2 = new int [7];
      for ( int i = 0; i < array.length; i++)
      {
         array2 [i] = Integer.parseInt (a);
      }
      int [ ] array3 = new int [7];
      boolean even = true;
      for ( int i = 0 ; i <array3.length ; i++)
      {
         even = !even;
         array3 [i] = decode ( array2 [i] , even);
      }

      int sum = 0;
      for ( int i = 0 ; i <array3.length ; i++)
      {
         sum = sum + array3 [i];
      }
      if ( sum % 10 == 0)
         return "The Card number is likely to be valid.";
      else
         return "The card number is not valid.";
   }
}