my one confusion in pro0

[skiesclear]

在类StdAudio中，我本想直接使用StdAudio.play(String filename);去播放一个音频，但是总是报错audio ./audio/2001.mid not found，并且在StdAudio源代码中play(String filename)函数中有这样一个报错AudioClip clip = Applet.newAudioClip(url);，很不幸这个问题我解决不了。
所以我换了一种方法：先用StdAudio.read(String filename)将音频文件读入后，利用StdAudio.play(double[] input)开始演奏，并且成功了。但是直接的方法却不可行令我很困惑，希望得到解答。

English:

In class StdAudio, I wanted to use StdAudio.play(String filename) to play a audio, but there are always errors audio ./audio/2001.mid not found, and there is a error in play(String filename) of StdAudio source code :AudioClip clip = Applet.newAudioClip(url);, and unfortunely I could't slove it.
so after thinking , I change a method: use StdAudio.read(String filename) to read audio file, and use StdAudio.play(double[] input) to play, and it do. but the confident method is no way, which confuse me.
please help me!