Generating unique random numbers and alphanumeric values in Java

Below code generates unique random numbers and alphanumeric values in Java.

Calendar date = Calendar.getInstance();
        String day = String.valueOf(date.get(Calendar.DAY_OF_MONTH));
        String month = String.valueOf(date.get(Calendar.MONTH)+1);
        String year = String.valueOf(date.get(Calendar.YEAR));

        if (day.length()==1){day = "0"+day;}
        if (month.length()==1){month = "0"+month;}

        String time =  String.valueOf(date.get(Calendar.HOUR_OF_DAY)) 

+ String.valueOf(date.get(Calendar.MINUTE)) +

 String.valueOf(date.get(Calendar.SECOND));

        System.out.println("Unique timeStamp is -> " + time +

 year + month + day);

        //Generates random hash string containing numbers and digits
        UUID id1 = UUID.randomUUID();
        System.out.println("Unique id is -> "+ id1);

        java.util.Date date1= new java.util.Date();
        System.out.println("Unique timestamp is -> " +

 new Timestamp(date1.getTime()));

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