@Testpublic void testFileReader() throws IOException {    File file = new File("D:/train/train.txt");    FileInputStream fs = new FileInputStream(file);    InputStreamReader reader = new InputStreamReader(fs,"utf8");    BufferedReader bufferedReader = new BufferedReader(reader);    System.out.println(bufferedReader.readLine());// 关闭文件流

bufferedReader.flush();

bufferedReader.close();

reader.close();fs.close();

}

@Testpublic void testFileOut() throws IOException {    File file = new File("D:/train/train.txt");    FileOutputStream out = new FileOutputStream(file);    String str = "hello world";    out.write(str.getBytes("utf8"));

out.close();

}

 /*** This abstract pathname's normalized pathname string. A normalized* pathname string uses the default name-separator character and does not* contain any duplicate or redundant separators.* 这个抽象路径的正常路径名称，"d:/program file/train"这种格式* @serial*/private final String path;/*** The length of this abstract pathname's prefix, or zero if it has no* prefix. 抽象路径的前缀长度，不存在则为0*/private final transient int prefixLength;

/*** Creates a new <code>File</code> instance by converting the given* pathname string into an abstract pathname.  If the given string is* the empty string, then the result is the empty abstract pathname.** @param   pathname  A pathname string* @throws  NullPointerException*          If the <code>pathname</code> argument is <code>null</code> 最通用给构造函数，通过文件路径来创建文件*/public File(String pathname) {if (pathname == null) {throw new NullPointerException();}this.path = fs.normalize(pathname);this.prefixLength = fs.prefixLength(this.path);}/*** Creates a new <code>File</code> instance from a parent pathname string* and a child pathname string.** <p> If <code>parent</code> is <code>null</code> then the new* <code>File</code> instance is created as if by invoking the* single-argument <code>File</code> constructor on the given* <code>child</code> pathname string.** <p> Otherwise the <code>parent</code> pathname string is taken to denote* a directory, and the <code>child</code> pathname string is taken to* denote either a directory or a file.  If the <code>child</code> pathname* string is absolute then it is converted into a relative pathname in a* system-dependent way.  If <code>parent</code> is the empty string then* the new <code>File</code> instance is created by converting* <code>child</code> into an abstract pathname and resolving the result* against a system-dependent default directory.  Otherwise each pathname* string is converted into an abstract pathname and the child abstract* pathname is resolved against the parent.* 通过父路径和子路径来创建文件* @param   parent  The parent pathname string* @param   child   The child pathname string* @throws  NullPointerException*          If <code>child</code> is <code>null</code>*/public File(String parent, String child) {if (child == null) {throw new NullPointerException();}if (parent != null) {if (parent.equals("")) {this.path = fs.resolve(fs.getDefaultParent(), -->"/"fs.normalize(child));} else {this.path = fs.resolve(fs.normalize(parent),fs.normalize(child));}} else {this.path = fs.normalize(child);}this.prefixLength = fs.prefixLength(this.path);}/** 通过父文件和子路径来创建文件* Creates a new <code>File</code> instance from a parent abstract* pathname and a child pathname string.** <p> If <code>parent</code> is <code>null</code> then the new* <code>File</code> instance is created as if by invoking the* single-argument <code>File</code> constructor on the given* <code>child</code> pathname string.** <p> Otherwise the <code>parent</code> abstract pathname is taken to* denote a directory, and the <code>child</code> pathname string is taken* to denote either a directory or a file.  If the <code>child</code>* pathname string is absolute then it is converted into a relative* pathname in a system-dependent way.  If <code>parent</code> is the empty* abstract pathname then the new <code>File</code> instance is created by* converting <code>child</code> into an abstract pathname and resolving* the result against a system-dependent default directory.  Otherwise each* pathname string is converted into an abstract pathname and the child* abstract pathname is resolved against the parent.** @param   parent  The parent abstract pathname* @param   child   The child pathname string* @throws  NullPointerException*          If <code>child</code> is <code>null</code>*/public File(File parent, String child) {if (child == null) {throw new NullPointerException();}if (parent != null) {if (parent.path.equals("")) {this.path = fs.resolve(fs.getDefaultParent(),fs.normalize(child));} else {this.path = fs.resolve(parent.path,   --> 将父文件转换成路径，然后和子路径拼接fs.normalize(child));}} else {this.path = fs.normalize(child);}this.prefixLength = fs.prefixLength(this.path);}