File:即常说的文件（I/O）储存方式，常用储存大量的数据，但缺点就是更新数据将是一件困难的事情。
下面的程序简单示范了如何读写应用数据文件夹中的文件。该程序的界面同样简单，只包含了两个文本输入框和两个按钮：其中第一组文本框和按钮用于处理输入；第二组文本框用于数据处理。其具体代码如下：
package com.ye_yun_lin.filetest;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.PrintStream;import javax.security.auth.PrivateCredentialPermission;import android.os.Bundle;import android.R.integer;import android.app.Activity;import android.view.Menu;import android.view.View;import android.view.View.OnClickListener;import android.widget.Button;import android.widget.EditText;public class MainActivity extends Activity { final String FILE_NAME = "MyData"; private EditText editText1; private EditText editText2; private Button button1; private Button button2; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); editText1=(EditText)findViewById(R.id.edittext1); button1=(Button)findViewById(R.id.button1); editText2=(EditText)findViewById(R.id.edittext2); button2=(Button)findViewById(R.id.button2); button1.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { write(editText1.getText().toString()); editText1.setText(""); } }); button2.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { editText2.setText(read()); } }); } private String read(){ try { FileInputStream fileInputStream=openFileInput(FILE_NAME); byte[] buff=new byte[1024]; int hasRead=0; StringBuilder sBuilder=new StringBuilder(""); while ((hasRead=fileInputStream.read(buff))>0) { sBuilder.append(new String(buff,0,hasRead)); } fileInputStream.close(); return sBuilder.toString(); } catch (Exception e) { e.printStackTrace(); } return null; } private void write(String content){ try { FileOutputStream fileOutputStream=openFileOutput(FILE_NAME, MODE_APPEND); PrintStream printStream=new PrintStream(fileOutputStream); printStream.println(content); printStream.close(); } catch (Exception e) { e.printStackTrace(); } }}
实例：SD卡文件浏览器：
当程序启动时，系统获取/mnt/sdcard目录下的全部文件、文件夹，并使用ListView将他们显示出来；当用户单击ListView的指定列表时，系统将会显示该列表下全部文件夹和文件。
该程序的界面布局文件如下：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent"> <TextView android:id="@+id/path" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentTop="true"/> <ListView android:id="@+id/list" android:layout_width="wrap_content" android:layout_height="wrap_content" android:divider="#000" android:dividerHeight="1px" android:layout_below="@id/path"> </ListView> <Button android:id="@+id/parent" android:layout_width="38dp" android:layout_height="34dp" android:background="@drawable/home" android:layout_centerHorizontal="true" android:layout_alignParentBottom="true"/></RelativeLayout>
主代码：
package com.ye_yun_lin.sdcard;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import android.os.Bundle;import android.R.integer;import android.app.Activity;import android.view.Menu;import android.view.View;import android.view.View.OnClickListener;import android.widget.AdapterView;import android.widget.AdapterView.OnItemClickListener;import android.widget.Button;import android.widget.ListView;import android.widget.SimpleAdapter;import android.widget.TextView;import android.widget.Toast;public class MainActivity extends Activity { private TextView textView; private ListView listView; private Button button; private File currentParent; private File[] currentFiles; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); textView=(TextView)findViewById(R.id.path); listView=(ListView)findViewById(R.id.list); button=(Button)findViewById(R.id.parent); File root=new File("/mnt/sdcard/"); if(root.exists()){ currentParent=root; currentFiles=root.listFiles(); inflateListView(currentFiles); } listView.setOnItemClickListener(new OnItemClickListener() { @Override public void onItemClick(AdapterView<?> parent, View view, int position, long id) { if(currentFiles[position].isFile()) return; File[] tmp=currentFiles[position].listFiles(); if(tmp==null || tmp.length==0){ Toast.makeText(MainActivity.this, "当前路径不可访问或该路径下没有文件", Toast.LENGTH_SHORT); } else{ currentParent=currentFiles[position]; currentFiles=tmp; inflateListView(currentFiles); } } }); button.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { try { if (!currentParent.getCanonicalPath().equals("/mnt/sdcard")) { currentParent=currentParent.getParentFile(); currentFiles=currentParent.listFiles(); inflateListView(currentFiles); } } catch (IOException e) { e.printStackTrace(); } } }); } private void inflateListView(File[] files){ List<Map<String,Object>> listItemsListView=new ArrayList<Map<String, Object>>(); for(int i=0;i<files.length;i++){ Map<String, Object> listItemMap=new HashMap<String, Object>(); if(files[i].isDirectory()){ listItemMap.put("icon", R.drawable.folder); }else{ listItemMap.put("icon", R.drawable.file); } listItemMap.put("fileName", files[i].getName()); listItemsListView.add(listItemMap); } SimpleAdapter simpleAdapter=new SimpleAdapter(this,listItemsListView,R.layout.line,new String[]{"icon","fileName"},new int[]{R.id.icon,R.id.file_name}); listView.setAdapter(simpleAdapter); try { textView.setText("当前路径为："+currentParent.getCanonicalPath()); } catch (IOException e) { e.printStackTrace(); } }}