Androidのファイル操作について

File file = new File(getFilesDir(), "hello.txt");
FileWriter fileWriter = null;

try {
  fileWriter = new FileWriter(file);
} catch (IOException e) {
  e.printStackTrace();
  return;
}

PrintWriter printWriter = new PrintWriter(new BufferedWriter(fileWriter));
printWriter.println("hello");
printWriter.close();

<?xml version="1.0" encoding="utf-8"?>
<manifest package="com.hiroom2.samplefile"
          xmlns:android="http://schemas.android.com/apk/res/android">

  <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
  <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

  <application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".SampleActivity">
      <intent-filter>
        <action android:name="android.intent.action.MAIN"/>

        <category android:name="android.intent.category.LAUNCHER"/>
      </intent-filter>
    </activity>
  </application>

</manifest> 

package com.hiroom2.samplefile;

import android.os.Bundle;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;

public class SampleActivity extends AppCompatActivity {

  private static final String gTag = "SampleActivity";

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

    Log.i(gTag, Environment.getExternalStorageDirectory().toString());
    Log.i(gTag, Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES).toString());
    Log.i(gTag, getExternalFilesDir(null).toString());
    Log.i(gTag, getExternalFilesDir(Environment.DIRECTORY_PICTURES).toString());
    Log.i(gTag, getExternalCacheDir().toString());
  }
}