MainActivity.java

package com.example.muskanhussain.honeydolist;

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

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class MainActivity extends AppCompatActivity {

    private EditText todoText;
    private Button saveButton;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        todoText = findViewById(R.id.todoText);
        saveButton = findViewById(R.id.saveButton);
        saveButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if(!todoText.getText().toString().equals(""))
                {
                    String message = todoText.getText().toString();
                    writeToFile(message);
                    Toast.makeText(MainActivity.this, "Saved!", Toast.LENGTH_LONG).show();
                }

            }
        });

        try {
            if(readFromFile() != null)
            {
                todoText.setText(readFromFile());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void writeToFile(String message)
    {
       try {
           OutputStreamWriter outputStreamWriter = new OutputStreamWriter(openFileOutput("todolist.txt",
                Context.MODE_PRIVATE));
                outputStreamWriter.write(message);
                outputStreamWriter.close();

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

    private String readFromFile() throws IOException {
        String result = "";
        InputStream inputStream = openFileInput("todolist.txt");
        if(inputStream != null)
        {
            InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
            BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
            String temp = "";
            StringBuilder stringBuilder = new StringBuilder();

            while((temp = bufferedReader.readLine()) != null)
            {
                stringBuilder.append(temp);
                stringBuilder.append("\n");
            }

            inputStream.close();
            result = stringBuilder.toString();
        }
        return result;
    }
}