Memory-leak android using arrays and files

I'm developing a dictionary using *.txt files in /raw directory, also I have a history (current 18 entries).

Every OnResume() I'm getting history entries from file on SDCard and filling ListArray 's than use ArrayAdapter to fill a ListView .

I can't understand why I have a big memory leak (every onResume() adds about 4-6 MB to the memory). Please help me.

Here is my code:

public class SecondTab extends Activity {

ListView lv1;

ArrayList <String> ArrayHist = new ArrayList <String>();

ArrayList <String> ArrayHistMin = new ArrayList <String>();

BufferedReader Buffer;

InputStream file;



/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.hist);



    SetContent();



    if (ru.andr.dictu.FirstTab.myErrorInHist)

    {

        Toast.makeText(this, getString(R.string.err_hist), Toast.LENGTH_LONG).show();

    }

}



public void SetContent()

{

    //show History entries

    //trying to solve memory leak

    try

    {

        ArrayHist.clear();

        ArrayHistMin.clear();

    }

    catch (Exception e){}

    ArrayHist=null;

    ArrayHistMin=null;

    ArrayHist = new ArrayList <String>();

    ArrayHistMin = new ArrayList <String>();

    Buffer=null;

    file=null;



if (ru.andr.dictu.FirstTab.myErrorInHist!=true) 

   {    

//filling arrays

    try {

        file = new FileInputStream(ru.andr.dictu.history_func.File_hist()); //getting name of file from common store

    } catch (FileNotFoundException e1) {

        // TODO Auto-generated catch block

        e1.printStackTrace();

    }

    Buffer = new BufferedReader(new InputStreamReader(file));

    try {

        String Str;

        int counter_hist_content = 0;

        while ( (Str = Buffer.readLine()) != null){ //reading from history file

                String myTrimStr = Str.trim();

                ArrayHistMin.add(myTrimStr.substring(0, myTrimStr.indexOf(";;")).intern()); //main word

                ArrayHist.add(myTrimStr.substring(myTrimStr.indexOf(";;")+2).intern()); //ususaly translate

                if (counter_hist_content==50) break;//needs only 50 entries



                counter_hist_content++;

             }

    } catch (IOException e) {

        // TODO Auto-generated catch block

        e.printStackTrace();

    }

    try

    {

        //closing files, buffers

        file.reset();

        file.close();

        Buffer.reset();

        Buffer.close();

    }catch (Exception e) {}



   }

    lv1 = (ListView)findViewById(R.id.history);

    lv1.setAdapter(new ArrayAdapter<String>(this, R.layout.list_item_hist, ArrayHistMin));

    lv1.setTextFilterEnabled(true);

    lv1.setOnItemClickListener(new OnItemClickListener() {

           public void onItemClick(AdapterView<?> a, View v, int position, long id) {

               changeClass (position , ArrayHist.get(position));



           }

    });



    lv1.setOnItemLongClickListener(new OnItemLongClickListener(){



        @Override

        public boolean onItemLongClick(AdapterView<?> arg0, View arg1,

                int arg2, long arg3) {

            // TODO Auto-generated method stub

            ru.andr.dictu.myspeak.text=null;

            ru.andr.dictu.myspeak.text=ArrayHistMin.get(arg2);



            if (ru.andr.dictu.myspeak.text.indexOf("[")!=-1)

            ru.andr.dictu.myspeak.text=ru.andr.dictu.myspeak.text.substring(0,ru.andr.dictu.myspeak.text.indexOf("[")).intern();

            speakClass();



            return true;

        }





    });

}



public void speakClass() {

    Intent intent = new Intent();

    intent.setClass(this, myspeak.class);

    startActivity(intent);

}



public void changeClass(int position, String extArray) {

    Intent intent = new Intent();

    intent.setClass(this, List.class);

    intent.putExtra(List.results, extArray.toString().intern());

    startActivity(intent);

    getParent().overridePendingTransition(R.anim.zoom_enter, R.anim.zoom_exit);

}

@Override  protected void onPause()  {super.onPause(); }

@Override

protected void onResume() 

{

    super.onResume();

    SetContent();

}