android设置铃声的时候f.mkdirs()创建不了？解决办法

android设置铃声的时候f.mkdirs()创建不了？？？
package com.yarin.android.Examples_07_08;

import java.io.File;

import android.app.Activity;
import android.content.Intent;
import android.media.RingtoneManager;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.widget.Button;
public class Activity01 extends Activity
{
/* 3个按钮 */
private Button mButtonRingtone;
private Button mButtonAlarm;
private Button mButtonNotification;

/* 自定义的类型 */
public static final int ButtonRingtone = 0;
public static final int ButtonAlarm = 1;
public static final int ButtonNotification = 2;
/* 铃声文件夹 */
// private String strRingtoneFolder = "/sdcard/music/ringtones";
// private String strAlarmFolder = "/sdcard/music/alarms";
// private String strNotificationFolder = "/sdcard/music/notifications";

private static final String strRingtoneFolder = Environment 

.getExternalStorageDirectory() 

+ "/music/ringtones"; 

private static final String strAlarmFolder = Environment 

.getExternalStorageDirectory() 


+ "/music/alarms"; 

private static final String strNotificationFolder = Environment 

.getExternalStorageDirectory() 

+ "/music/notifications"; 




/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

mButtonRingtone = (Button) findViewById(R.id.ButtonRingtone);
mButtonAlarm = (Button) findViewById(R.id.ButtonAlarm);
mButtonNotification = (Button) findViewById(R.id.ButtonNotification);
/* 设置来电铃声 */
mButtonRingtone.setOnClickListener(new Button.OnClickListener() 
{
@Override
public void onClick(View arg0)
{
System.out.println("111111111111");
if (bFolder(strRingtoneFolder))
{
System.out.println("111111111111");
//打开系统铃声设置
Intent intent = new Intent(RingtoneManager.ACTION_RINGTONE_PICKER);
//类型为来电RINGTONE
intent.putExtra(RingtoneManager.EXTRA_RINGTONE_TYPE, RingtoneManager.TYPE_RINGTONE);
//设置显示的title
intent.putExtra(RingtoneManager.EXTRA_RINGTONE_TITLE, "设置来电铃声");
//当设置完成之后返回到当前的Activity
startActivityForResult(intent, ButtonRingtone);
}
}
});
/* 设置闹钟铃声 */
mButtonAlarm.setOnClickListener(new Button.OnClickListener() 
{
@Override
public void onClick(View arg0)
{
if (bFolder(strAlarmFolder))
{
//打开系统铃声设置
Intent intent = new Intent(RingtoneManager.ACTION_RINGTONE_PICKER);
//设置铃声类型和title
intent.putExtra(RingtoneManager.EXTRA_RINGTONE_TYPE, RingtoneManager.TYPE_ALARM);
intent.putExtra(RingtoneManager.EXTRA_RINGTONE_TITLE, "设置闹铃铃声");
//当设置完成之后返回到当前的Activity
startActivityForResult(intent, ButtonAlarm);
}
}
});
/* 设置通知铃声 */
mButtonNotification.setOnClickListener(new Button.OnClickListener() 
{
@Override
public void onClick(View arg0)
{
if (bFolder(strNotificationFolder))
{
//打开系统铃声设置
Intent intent = new Intent(RingtoneManager.ACTION_RINGTONE_PICKER);
//设置铃声类型和title
intent.putExtra(RingtoneManager.EXTRA_RINGTONE_TYPE, RingtoneManager.TYPE_NOTIFICATION);
intent.putExtra(RingtoneManager.EXTRA_RINGTONE_TITLE, "设置通知铃声");
//当设置完成之后返回到当前的Activity