I would try to project your geometry into a spatial reference with a managable unit (like metres)
So my polygon below is in WGS84. I project it into web mercator and then I have a more useful area unit
Polygon polygon = new Polygon();
polygon.startPath(25, 5.59);
polygon.lineTo(13.42, 3.92);
polygon.lineTo(12.3, 23.3);
polygon.lineTo(38.2, 22.9);
polygon.closePathWithLine();
SimpleLineSymbol outline = new SimpleLineSymbol(
new Color(0, 200, 0), 3, SimpleLineSymbol.Style.DASH_DOT_DOT);
SimpleFillSymbol symbol = new SimpleFillSymbol(new Color(200, 0, 0, 120), outline);
Graphic graphic = new Graphic(polygon, symbol);
graphicsLayer.addGraphic(graphic);
//web mercator works in meters
SpatialReference webMercator = SpatialReference.create(3857);
//project from wgs84 into web mercator
Polygon newPoly = (Polygon) GeometryEngine.project(polygon, map.getSpatialReference(), webMercator);
double area = newPoly.calculateArea2D();
//now you have an easier unit of meature to play with
System.out.println("Area is " + area + webMercator.getUnit().getName() + " squared");