Extract  numbers from a string

Character.isDigit(str.charAt(i))
Character.isLetter(str.charAt(i))
Character.isAlphabetic(str.charAt(i))

String password = "cnE4g1Z5y9A";    
String[] letters= password.split("[0-9]");    ==> cnEgZyA
String[] letters= password.split("[A-Za-z]");    ==> 4159