public static String getNextUpEn(String en){ char lastE = 'a'; char st = en.toCharArray()[0]; if(Character.isUpperCase(st)){ if(en.equals("Z")){ return "A"; } if(en==null || en.equals("")){ return "A"; } lastE = 'Z'; }else{ if(en.equals("z")){ return "a"; } if(en==null || en.equals("")){ return "a"; } lastE = 'z'; } int lastEnglish = (int)lastE; char[] c = en.toCharArray(); if(c.length>1){ return null; }else{ int now = (int)c[0]; if(now >= lastEnglish) return null; char uppercase = (char)(now+1); return String.valueOf(uppercase); } }