The document contains code for multiple Android activities that calculate various mathematical operations and conversions by taking user input from edit texts, performing calculations, and displaying outputs in text views. The activities include subtraction of 3 numbers, perimeter calculations for polygons, unit conversions between meters to centimeters, etc. The code follows a similar structure for each activity of getting references to edit texts and text views, parsing user input, performing calculations, and setting the text view to the output.