sp记住账户名

package com.example.lenovo.lianxiyong;

import android.content.SharedPreferences;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class JizhuzhanghaoActivity extends AppCompatActivity {

    EditText et1;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_jizhuzhanghao);

        et1=(EditText)findViewById(R.id.et1);

        SharedPreferences sp=getSharedPreferences("a",MODE_PRIVATE);

        String s=sp.getString("a",null);
        et1.setText(s);
    }

    public void bt1(View v)
    {
        String string=et1.getText().toString();
        SharedPreferences sharedPreferences=getSharedPreferences("a",MODE_PRIVATE);

        SharedPreferences.Editor editor=sharedPreferences.edit();

        editor.putString("a",string);

        editor.commit();

        Toast.makeText(JizhuzhanghaoActivity.this, "记住账户", Toast.LENGTH_SHORT).show();
    }
}