生成一个唯一的6位字符编码（到2063年前一直生效）的JAVA 方法

public String unRepeatSixCode() {
String sixChar = "";
SimpleDateFormat sdf = new SimpleDateFormat("yyMMddHHmmss");
Date date = new Date();
String time = sdf.format(date);
for (int i = 0; i < time.length() / 2; i++) {
String singleChar;
String x = time.substring(i * 2, (i + 1) * 2);
int b = Integer.parseInt(x);
if (b < 10) {
singleChar = Integer.toHexString(Integer.parseInt(x));
} else if (b >= 10 && b < 36) {
singleChar = String.valueOf((char) (Integer.parseInt(x) + 55));
} else {
singleChar = String.valueOf((char) (Integer.parseInt(x) + 61));
}
sixChar = sixChar + singleChar;

}
System.out.println("生成一个6位不可重复的字符编码是：" + sixChar);
return sixChar;


}