How to check if latitude and longitude is inside given extents?

Question

I am using arcgis map for offline map in my Android application, so I have downloaded a map with some extent values i.e.

{
  "xmin" : -12699130, 
  "ymin" : 3988230, 
  "xmax" : -12699130, 
  "ymax" : 5178858,
  "spatialReference" : {
    "wkid" : 3857
  }
}

Now I want to apply my logic like this:

1. Let xy be some lat/long
2. If xy is in specified extent area as mentioned above (means is in the area which I have downloaded)
3. Only then open the arcgis map otherwise open skobbler map (using for offline street map), same as arcgis offline map but only provide street view.

I tried some code like this below:

//First set the extent and made a envelope
Envelope extentForTPK = new Envelope();
extentForTPK.setCoords(-12699130,3988230,-12699130,5178858);

//Then created a point from lat/long and checking if the point is inside the envelope(ie extentForTpk)
Point wgspoint=new Point(lat, long);

Problem:

First, I am unable to convert lat/long to the points so I think this might be the problem.

Second, I am now inflating the MapView and trying mMapView.getSpatialReference() function call.

Finally, my whole process for checking is wrong.