code: public static String random(int count, RandomType randomType) {
  		if (count == 0) return "";
  		if (count < 0) {
  			throw new IllegalArgumentException("Requested random string length " + count + " is less than 0.");
  		}
  		char[] buffer = new char[count];
  		for (int i = 0; i < count; i++) {
  			if (randomType.equals(RandomType.INT)) {
  				buffer[i] = _INT.charAt(RANDOM.nextInt(_INT.length()));
  			} else if (randomType.equals(RandomType.STRING)) {
  				buffer[i] = _STR.charAt(RANDOM.nextInt(_STR.length()));
  			}else {
  				buffer[i] = _ALL.charAt(RANDOM.nextInt(_ALL.length()));
  			}
  		}
  		return new String(buffer);
  	}
docs: 随机数生成
  @param count
  @return {String}