ListView use SimpleAdapter

MainActivity.java :

package com.main;


import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

import com.example.sample_listview.R;

import android.app.Activity;
import android.os.Bundle;
import android.widget.ListView;
import android.widget.SimpleAdapter;

public class MainActivity extends Activity {
 ListView lv;
 SimpleAdapter sa;
 ArrayList<Map<String, Object>> mapArray = new ArrayList<Map<String, Object>>();
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  // TODO Auto-generated method stub
  super.onCreate(savedInstanceState);
  this.setContentView(R.layout.main);
  //initialize the list view
  lv = (ListView) this.findViewById(R.id.listView1);
  sa = new SimpleAdapter(this, mapArray, R.layout.main_list, 
    new String[]{"DisplayString"}, 
    new int[]{R.id.textView1});
  lv.setAdapter(sa);
  lv.setStackFromBottom(true);//display from bottom
  //generate the test string array
  String[] testString = new String[5000];
  for(int i=0;i<testString.length;i++){
   testString[i] = "test string "+i;
  }
  //put string in the map of list
  for(int i=0;i<testString.length;i++){
   Map<String, Object> map = new HashMap<String, Object>();
   map.put("DisplayString", testString[i]);
   mapArray.add(map);
  }  
 }
}

main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <ListView
        android:id="@+id/listView1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" >
    </ListView>

</LinearLayout>

main_list.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="TestString"
        android:textSize="30sp" />

</LinearLayout>