1. Convert S2Cell Id to Latitude and Longitude

To get the Latitude and Longitude of given S2cell Id, below is the code,

public List < String > getLatLong(String s2Id) {
    List < String > latlong = new ArrayList < > ();
    if (s2Id == null) {
        Assert.fail("Invalid S2Id provided");
    }
    S2CellId cell = new S2CellId(Long.parseLong(s2Id));
    double latitude = cell.toLatLng().lat().degrees();
    double longitude = cell.toLatLng().lng().degrees();
    latlong.add(String.valueOf(latitude));
    latlong.add(String.valueOf(longitude));
    return latlong;
}

2. Convert Latitude and Longitude to S2Cell Id

To get the S2cell Id of given Latitude and Longitude below is the code,

public String getS2Id(String latitude, String longitude) {
    if ((latitude == null || latitude.isEmpty()) || (longitude == null || longitude.isEmpty())) {
        Assert.fail("Invalid latitude/longitude provided");
    }
    S2LatLng s2LatLng = S2LatLng.fromDegrees(Double.parseDouble(latitude), Double.parseDouble(longitude));
    return String.valueOf(S2CellId.fromLatLng(s2LatLng).id());
}