Android Studio Convert ISO string to “America/New_York” when adding to event to calendar

That is because you’re telling the parser to ignore the Z, or rather to match it literally, but not to process it’s meaning.

The input strings are Instant values, so parse to Instant, then apply time zone.
If you don’t have Java 8+ compatible Android, use ThreeTenABP.

String stTime = "2018-10-17T22:00:00Z";

ZonedDateTime time = Instant.parse(stTime).atZone(ZoneId.of("America/New_York"));
System.out.println(time); // prints: 2018-10-17T18:00-04:00[America/New_York]

If you prefer using antiquated SimpleDateFormat, simply use the correct format, and don’t specify time zone.

SimpleDateFormat formatStart = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssX");
Date startDate = formatStart.parse(stTime);
// My default time zone is America/New_York, so:
System.out.println(startDate); // prints: Wed Oct 17 18:00:00 EDT 2018

startDate.getTime() is the time-in-millis you need.

For API Level < 24, format pattern X doesn’t work, so you need to do the hardcoded Z like in your question, but tell the parser that it is in UTC, because that is what the Z time zone means.

SimpleDateFormat formatStart = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'");
formatStart.setTimeZone(TimeZone.getTimeZone("UTC"));
Date startDate = formatStart.parse(stTime);
// My default time zone is America/New_York, so:
System.out.println(startDate); // prints: Wed Oct 17 18:00:00 EDT 2018