android 记住密码

package com.example.helloword; 
import android.app.Activity;  

 import android.content.SharedPreferences;  

 import android.os.Bundle;  

 import android.text.Editable;  

 import android.text.InputType;  

 import android.text.TextWatcher;  

 import android.view.View;  

 import android.view.View.OnClickListener;  

 import android.widget.ArrayAdapter;  

 import android.widget.AutoCompleteTextView;  

 import android.widget.Button;  

 import android.widget.CheckBox;  

 import android.widget.EditText;  

 import android.widget.Toast;  

    

 public class MainActivity  extends Activity {  

    

     AutoCompleteTextView cardNumAuto;  

     EditText passwordET;  

     Button logBT;  

    

     CheckBox savePasswordCB;  

     SharedPreferences sp;  

     String cardNumStr;  

     String passwordStr;  

    

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

     @Override 

     public void onCreate(Bundle savedInstanceState) {  

         super.onCreate(savedInstanceState);