class ReadWriteActivity

package com.example.choi.ex04_file;

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

import java.io.BufferedReader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.InputStreamReader;

public class ReadWriteActivity extends AppCompatActivity {

    //1.변수선언
    Button btnSave, btnLoad, btnDelete;
    EditText edit1;

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

        //2.위젯 연결
        btnSave =(Button)findViewById(R.id.btnSave);
        btnLoad=(Button)findViewById(R.id.btnLoad);
        btnDelete=(Button)findViewById(R.id.btnDelete);
        edit1=(EditText)findViewById(R.id.edit1);

        //3.저장 버튼
        btnSave.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
        // /data/data/패키지이름/files => 내장 메모리 전용 디렉토리

                File file =new File("/data/data/com.example.choi.ex04_file/files/test.txt");
                try{
//스트림 - 1바이트 단위 입출
// Reader, Writer 문자 단위 입출력
                    FileOutputStream fos =new FileOutputStream(file);
                    // 사용자가 입력한 내용
                    String str =edit1.getText().toString();
                    //바이트배열로 변환하여 저장
                    fos.write(str.getBytes());
                    fos.close();//스트림 닫기
                    Toast.makeText(ReadWriteActivity.this,
                            "저장되었습니다.", Toast.LENGTH_LONG).show();
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        });



        //4. 불러오기 버튼 클릭
        btnLoad.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try{
                 // opendFileInput() 내장 메모리의 파일 오픈
                 // /data/data/패키지이름/files
                    InputStream is=openFileInput("test.txt");
                    if(is!=null){
                        //스트림을 리더로(문자 단위, 한글 처리)
                        InputStreamReader reader=
                                new InputStreamReader(is, "utf-8");
                        BufferedReader br =new BufferedReader(reader);
                        String str="";
                        StringBuffer sb =new StringBuffer();
                   //br.readLine() 버퍼에서 한 라인을 읽음
                        while ((str =br.readLine()) !=null){
                            sb.append(str +"\n"); //개행문자 추가
                        }
                        is.close(); //스트림 닫기
                        edit1.setText(sb.toString());
                    }
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        });



        //5. 삭제하기
        btnDelete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
//내장 메모리의 파일 삭제
                    deleteFile("test.txt");

// Toast.LENGTH_LONG 2~3초
// Toast.LENGTH_SHORT 1 ~ 2초

                Toast.makeText(ReadWriteActivity.this, "삭제되었습니다.",
                        Toast.LENGTH_LONG).show();



            }
        });



    }







}

 

read_write.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/read_write"
    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.choi.ex04_file.ReadWriteActivity">

    <Button
        android:text="저장"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:id="@+id/btnSave" />

    <Button
        android:text="불러오기"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:id="@+id/btnLoad" />

    <Button
        android:text="삭제"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true"
        android:id="@+id/btnDelete" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="textMultiLine"
        android:ems="10"
        android:id="@+id/edit1"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentBottom="true"
        android:layout_below="@+id/btnSave" />

</RelativeLayout>