mainActivity

package com.example.filepersistencetest;

import android.content.Context;
import android.net.Uri;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.text.TextUtils;
import android.widget.EditText;
import android.widget.Toast;

import com.google.android.gms.appindexing.Action;
import com.google.android.gms.appindexing.AppIndex;
import com.google.android.gms.appindexing.Thing;
import com.google.android.gms.common.api.GoogleApiClient;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class MainActivity extends AppCompatActivity {
    private EditText edit;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        edit = (EditText) findViewById(R.id.edit);
        String inputText=load();
        if(!TextUtils.isEmpty(inputText))
        {
            edit.setText(inputText);
            edit.setSelection(inputText.length());
            Toast.makeText(this,"succeeded",Toast.LENGTH_SHORT).show();

        }
    }



    protected void onDestroy() {
        super.onDestroy();
        String inputText = edit.getText().toString();//toString
        save(inputText);
    }
    public String load(){
        FileInputStream inputStream=null;
        BufferedReader reader=null;

        StringBuilder content=new StringBuilder();
        try {
            inputStream=openFileInput("data");
         reader=new BufferedReader( new InputStreamReader(inputStream));
        String line="";
            while ((line=reader.readLine())!=null) {
                content.append(line);

            }
        }catch (IOException e){
            e.printStackTrace();
        }finally {
            if(reader!=null){
                try{
                    reader.close();

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

        return content.toString();
    }




    public void save(String inputText)
    {
        FileOutputStream out =null;
        BufferedWriter writer=null;
        try{
            out=openFileOutput("data", Context.MODE_PRIVATE);
            writer= new BufferedWriter( new OutputStreamWriter(out));
            writer.write(inputText);

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

        }finally {
            try {
                if(writer!=null){
                    writer.close();

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



}
 

main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.filepersistencetest.MainActivity">

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/edit"
        android:hint="Type something here"
        />
</RelativeLayout>