You can do this:
Paint paint = new Paint();
final RectF rect = new RectF();
//Example values
rect.set(mWidth/2- mRadius, mHeight/2 - mRadius, mWidth/2 + mRadius, mHeight/2 + mRadius);
paint.setColor(Color.GREEN);
paint.setStrokeWidth(20);
paint.setAntiAlias(true);
paint.setStrokeCap(Paint.Cap.ROUND);
paint.setStyle(Paint.Style.STROKE);
canvas.drawArc(rect, -90, 360, false, paint);
The key is in paint.setStyle(Paint.Style.STROKE);
, it crops the arc’s center with the stroke that you define in setStrokeWidth (in the example draws an arc with a radius of mRadius and 20px thick).
Hope it helps!