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);
    }

}