Pure Java random string code to Processing random string code

Processing Coding Questions
3 
void setup()
{
  int n =  20 ;
  System.out.println(getAlphaNumericString(5));
}

String getAlphaNumericString(int n)
{
  public class RandomString {



    // chose a Character random from this String

    String AlphaNumericString =  "ABCDEFGHIJKLMNOPQRSTUVWXYZ"

      +  "0123456789"

      +  "abcdefghijklmnopqrstuvxyz" ;



    // create StringBuffer size of AlphaNumericString

    StringBuilder sb =  new StringBuilder(n);

    for ( int i =  0; i < n; i++) {



      // generate a random number between

      // 0 to AlphaNumericString variable length

      int index

        = ( int )(AlphaNumericString.length()

        * Math.random());



      // add Character one by one in end of sb

      sb.append(AlphaNumericString

        .charAt(index));
    }



    return sb.toString();
  }



  public static void main(String[] args)

  {



    // Get the size n

    int n =  20 ;



    // Get and display the alphanumeric string

    System.out.println(RandomString.getAlphaNumericString(n));
  }
}

With this code, I get “expecting {, found ‘for’”