案例：

activity_main.xml

MainActivity.java

package com.example.administrator.filemanager; import android.app.Activity; import android.content.Context; import android.os.Bundle; import android.os.Environment; import android.support.v7.app.ActionBarActivity; import android.text.method.ScrollingMovementMethod; import android.view.Menu; import android.view.MenuItem; import android.view.View; import android.widget.TextView; import android.widget.Toast; import java.io.File; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.io.PrintStream; public class MainActivity extends Activity {
       private TextView textView;     @Override     protected void onCreate(Bundle savedInstanceState) {
           super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);         textView = (TextView) findViewById(R.id.textView);         textView.setTextSize(14);     }     /*写入私有文件*/     public void writePrivateFileClick(View view) {
           try {
               //Context.MODE.PRIVATE 创建私有文件 APPEND是增加内容             OutputStream out = openFileOutput("xfei.txt", Context.MODE_APPEND);             String info = "我是中国人";             byte[] bytes = info.getBytes();             out.write(bytes, 0, bytes.length);             out.close();         } catch (FileNotFoundException e) {
               e.printStackTrace();         } catch (IOException e) {
               e.printStackTrace();         }     }     /*读取私有文件*/     public void readPrivateFileClick(View view) {
           try {
               InputStream in = openFileInput("xfei.txt");             byte[] bytes = new byte[1024];             StringBuffer sb = new StringBuffer();             int len = -1;             while ((len = in.read(bytes)) != -1) {
                   sb.append(new String(bytes, 0, len));             }             in.close();             textView.setText("  " + sb);             //  Toast.makeText(this,sb,Toast.LENGTH_SHORT).show();         } catch (FileNotFoundException e) {
               e.printStackTrace();         } catch (IOException e) {
               e.printStackTrace();         }     }     //读取目录raw下的文件     public void readRAWFileClick(View view) {
           try {
               InputStream in = getResources().openRawResource(R.raw.xfei);             byte[] bytes = new byte[1024];             StringBuffer sb = new StringBuffer();             int len = -1;             while ((len = in.read(bytes)) != -1) {
                   sb.append(new String(bytes, 0, len));             }             in.close();             // Toast.makeText(this,sb,Toast.LENGTH_SHORT).show();             textView.setText("  " + sb);             textView.setMovementMethod(ScrollingMovementMethod.getInstance());         } catch (FileNotFoundException e) {
               e.printStackTrace();         } catch (IOException e) {
               e.printStackTrace();         }     }     //写入一个内部私有缓存文件     public void writePrivateCacheDataClick(View view) {
           //创建一个缓存的文件         //String temp= getCacheDir()+"/temp.tmp";         //System.out.println();         try {
               File temp = File.createTempFile("temp", null, getCacheDir());             FileOutputStream out = new FileOutputStream(temp);             PrintStream ps = new PrintStream(out);             ps.print("我可是要成为编程王的男人");             ps.close();             out.close();         } catch (IOException e) {
               e.printStackTrace();         }     }     public void isSDCardClick(View view) {
           //判断是否有SD卡         if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
               Toast.makeText(this, "有SD卡", Toast.LENGTH_SHORT).show();             if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED_READ_ONLY)) {
                   Toast.makeText(this, "SDCard只读", Toast.LENGTH_SHORT).show();             } else {//sdcard路径                 System.out.println(Environment.getExternalStorageDirectory().getPath());                 //访问android内置的文件夹                 System.out.println(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS));             }         } else {
               Toast.makeText(this, "没有SD卡", Toast.LENGTH_SHORT).show();         }     }     //写SD卡私有文件     public void writeSDcardPrivateFileClick(View view) {
           //获得路径         File file = getExternalFilesDir(null);         if (file != null) {
               try {
                   FileOutputStream out = new FileOutputStream(file + "/xfei.txt");                 PrintStream ps = new PrintStream(out);                 ps.print("今天吃药没？");                 ps.close();                 out.close();             } catch (FileNotFoundException e) {
                   e.printStackTrace();             } catch (IOException e) {
                   e.printStackTrace();             }         }     }       //写入SD卡 私有缓存文件     public void writeSDcardPrivateCacheFileClick(View v) {
           try {
              File temp= File.createTempFile("xfei",null,getExternalCacheDir());             if (temp != null) {
                       FileOutputStream out = new FileOutputStream(temp);                     PrintStream ps = new PrintStream(out);                     ps.print("今天吃药没？给你药吃");                     ps.close();                     out.close();             }         } catch (IOException e) {
               e.printStackTrace();         }     } }