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PONullPointerException in class
 

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    <p>I have a class that contains 2 functions:</p> <pre><code>public class FileHandler extends Activity { public void writeToFile(){ String fileName = "lastDevice.txt"; try { FileOutputStream fos = openFileOutput(fileName, MODE_PRIVATE); //Exception thrown here fos.write("some device id".getBytes()); fos.close(); Toast.makeText(this, "File updated", Toast.LENGTH_SHORT).show(); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public String readFromFile(){ try { String fileName = "lastDevice.txt"; FileInputStream fis = openFileInput(fileName); //Exception thrown here InputStreamReader isr = new InputStreamReader(fis); BufferedReader br = new BufferedReader(isr); String sLine = null; String data =""; while ((sLine = br.readLine())!=null) { data+= sLine; } return data; } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); return "FileNotFoundException"; } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); return "IOException"; } catch (NullPointerException e){ // TODO Auto-generated catch block e.printStackTrace(); return "Null Pointer Exception"; } } </code></pre> <p>these functions are called from my main activity as follows:</p> <pre><code>@Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); lvDevices = (ListView)findViewById(R.id.ListViewDevices); lastDeviceTxt = (TextView)findViewById(R.id.lastDeviceTxt); //get last connected device FileHandler fh = new FileHandler(); String last = fh.readFromFile(); lastDeviceTxt.setText(last); } </code></pre> <p>but i keep getting a <code>NullPointerException</code> from both functions.<br> when running the functions from my <code>MainActivity</code> (I copied them to my main activity) they work fine. What am I doing wrong? (please remember that I'm very new to <code>android</code> development).</p>
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    1. CO*i keep getting a NullPointerException from both functions* => On what line is the exception thrown?
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    3. COgetDateTime gdt = new getDateTime(); what does this mean ?
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