Create A Program Using Accelerometers

I have to create a program using accelerometers. I have written these pieces of code in order to start recording the accelerometer data when you push start, stopping when you press stop and then saving that in a file called data1.csv and so on (data2,3 4 etc). The reason I want to do this is so that I can look at the data for a given gesture and analyse it using graphs and other simple methods.

The issue I'm having is this program just makes random empty files - doesnt seem to log the data. It does make each file though, so that's nice

Code:
package com.test.Acceltest;
import java.util.List;
import android.app.Activity;
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorManager;
[code]...