为什么我无法调试sun.nio.cs.StreamDecoder

Question

我想调试代码InputStreamReader reader = new InputStreamReader(new FileInputStream(filename)); 当我断点时，我无法输入源代码

    /**
 * Creates an InputStreamReader that uses the default charset.
 *
 * @param  in   An InputStream
 */
public InputStreamReader(InputStream in) {
    super(in);
    try {
        sd = StreamDecoder.forInputStreamReader(in, this, (String)null); // ## check lock object
    } catch (UnsupportedEncodingException e) {
        // The default encoding should always be available
        throw new Error(e);
    }
}

我有附件并下载了许多版本的源代码。 谁能帮帮我，谢谢。