SharedPreferences存取应用程序访问时间

package com.example.sharepre1;

import java.util.Date;

import android.os.Bundle;
import android.app.Activity;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.view.Menu;
import android.widget.TextView;

public class MainActivity extends Activity {
private TextView showtime;
private static final String FILENAME = "time";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
showtime = (TextView) findViewById(R.id.showtime);
SharedPreferences preferences = getSharedPreferences(FILENAME,0);
String lasttime = preferences.getString("time", null);

if(lasttime==null){
lasttime = "第一次使用本应用程序";
}else{
lasttime = "你上次访问的时间为"+lasttime;
}
Editor editor = preferences.edit();
editor.putString("time", new Date().toLocaleString());
editor.commit();
showtime.setText(lasttime);
}

}