Java program to generate a complex alphanumeric password.

public class RandomString {      
 // Creates random string    
          public static String randomstring(int lo, int hi){      
                  int n = rand(lo, hi);      
                  byte b[] = new byte[n];      
                  for (int i = 0; i < n; i++)      
                          b[i] = (byte)rand('a', 'z');      
                  return new String(b, 0);      
          }      
     
          private static int rand(int lo, int hi){      
                      java.util.Random rn = new java.util.Random();      
                  int n = hi - lo + 1;      
                  int i = rn.nextInt(n);      
                  if (i < 0)      
                          i = -i;      
                  return lo + i;      
          }      
     
          public static String randomstring(){      
                  return randomstring(5, 25);      
          }      
     
        /**    
         * @param args    
         */     
        public static void main(String[] args) {      
                System.out.println(randomstring());      
     
        }      
     
}