Alarm is setting earlier time for example current time is 3:00 pm if I set 2:00 pm it is going to be ring within a minute

Question

Alarm is not ringing on exact time and it is allowing to set in the pas time it should be set for the future not to less than current time I have tried logics but did not worked.

case R.id.alarm_on:
//setting calendar instance with the hour and minute that we picked
// on the timepicker

calendar.set(Calendar.HOUR_OF_DAY, alarm_timepicker.getHour());
calendar.set(Calendar.MINUTE, alarm_timepicker.getMinute());


getting integer value of hour and time
int hour = alarm_timepicker.getHour();
int minute = alarm_timepicker.getMinute();


convert the int values into strings
String hour_string = String.valueOf(hour);
String minute_string = String.valueOf(minute);


txthour.setText(hour_string);
txtminute.setText(minute_string);

convert into 12 hour format

if (hour > 12) {
hour_string = String.valueOf(hour - 12);
}
if (minute < 10) {
minute_string = "0" + String.valueOf(minute);
}

//METHOD THAT CHANGE THE UPDATE TEXTBOX
set_alarm_text("Alarm set to " + hour_string + ":" + minute_string);

//put extra string into my_intent
//tells the clock that you pressed the alarm button_on
my_intent.putExtra("extra", "alarm on");

//put extra long into my_intent
//tells the clock that you want a certain value from the dropdown menu 

my_intent.putExtra("whale_choice", choose_whale_sound);
//create the pending intent that delays the intent
//until the specified calendar time




pending_Intent = PendingIntent.getBroadcast(MainActivity.this, 0, my_intent,
PendingIntent.FLAG_UPDATE_CURRENT);

setting the alarm manager

alarm_manager.setExact(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pending_Intent);