package com.example.pengtuanyuan.logindemo01;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;


public class UserInfoUtil {
    public static Boolean saveUserInfo(String useName, String usePassword) {


        try {
            String userInfo=useName+"##"+usePassword;
            String path="/data/data/com.example.pengtuanyuan.logindemo01";
            File file=new File(path,"userInfo.txt");
            FileOutputStream fileOutputStream=new FileOutputStream(file);
            fileOutputStream.write(userInfo.getBytes());
            fileOutputStream.close();
            return true;

        } catch (IOException e) {
            e.printStackTrace();
        }

        return false;
    }
    public static Map<String,String> getUserInfo(){

        try {
            String path="/data/data/com.example.pengtuanyuan.logindemo01";
            File file=new File(path,"userInfo.txt");
            FileInputStream fileInputStream=new FileInputStream(file);
            BufferedReader bufferedReader= new BufferedReader(new InputStreamReader(fileInputStream));
            String readLine =bufferedReader.readLine();
            String[] split=readLine.split("##");
            HashMap<String,String> hashMap=new HashMap<String,String>();

            hashMap.put("useName",split[0]);
            hashMap.put("usePassword",split[1]);
            bufferedReader.close();
            fileInputStream.close();

            return hashMap;


        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;


    }
}
----------------------------------------------------
package com.example.pengtuanyuan.logindemo01;

import android.content.Context;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.Toast;

import java.util.Map;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

    private EditText ed_inputName;
    private EditText ed_inputPassword;
    private CheckBox cb_choice;
    private Button bt_login;
    private Context mContext;


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


        mContext=this;

        ed_inputName = (EditText) findViewById(R.id.ed_inputName);
        ed_inputPassword = (EditText) findViewById(R.id.ed_inputPassword);
        cb_choice = (CheckBox) findViewById(R.id.cb_choice);
        bt_login = (Button) findViewById(R.id.bt_login);

        bt_login.setOnClickListener(this);


        Map<String,String> map=UserInfoUtil.getUserInfo();
        if (map!=null){
            String userName=map.get("useName");
            String password=map.get("usePassword");
            ed_inputName.setText(userName);
            ed_inputPassword.setText(password);
        }
    }

    private void login(){

        String useName = ed_inputName.getText().toString().trim();
        String usePassword = ed_inputPassword.getText().toString().trim();
        boolean isChecked=cb_choice.isChecked();

        if (TextUtils.isEmpty(useName)||TextUtils.isEmpty(usePassword)){
            Toast.makeText(mContext,"Name and password cannot be empty",Toast.LENGTH_SHORT).show();
            return;
        }
        if (isChecked){
            Boolean result=UserInfoUtil.saveUserInfo(useName,usePassword);
            if (result){
                Toast.makeText(mContext,"Name and password be saved",Toast.LENGTH_SHORT).show();
            }else{
                Toast.makeText(mContext,"Name and password cannot be saved",Toast.LENGTH_SHORT).show();
            }
        }else {
            Toast.makeText(mContext,"Name and password don't need to be saved",Toast.LENGTH_SHORT).show();
        }

    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.bt_login:
                login();
                break;
            default:
                break;
        }

    }
}