Java 日看一类（18）之IO包中的FileNameFilter接口类和FileNotFoundException异常类

FileNameFilter接口未引入任何包

该类类头注释如下：

/**
 * Instances of classes that implement this interface are used to
 * filter filenames. These instances are used to filter directory
 * listings in the <code>list</code> method of class
 * <code>File</code>, and by the Abstract Window Toolkit's file
 * dialog component.
 *
 * @author  Arthur van Hoff
 * @author  Jonathan Payne
 * @see     java.awt.FileDialog#setFilenameFilter(java.io.FilenameFilter)
 * @see     java.io.File
 * @see     java.io.File#list(java.io.FilenameFilter)
 * @since   JDK1.0
 */

大意如下：

实现该接口的类可对文件名进行过滤

Abstract Window Toolkit 的文件对话框组件使用这些实例过滤File类的list方法中的目录清单

仅含有一个成员方法：

检测特定的文件是否存在于该文件列表中（dir中为文件所在目录，string为文件名

boolean accept(File dir, String name);

该类十分简单，不再过多叙述

FileNotFoundException异常类继承自IOException

类头注释如下：

/**
 * Signals that an attempt to open the file denoted by a specified pathname
 * has failed.
 *
 * <p> This exception will be thrown by the {@link FileInputStream}, {@link
 * FileOutputStream}, and {@link RandomAccessFile} constructors when a file
 * with the specified pathname does not exist.  It will also be thrown by these
 * constructors if the file does exist but for some reason is inaccessible, for
 * example when an attempt is made to open a read-only file for writing.
 *
 * @author  unascribed
 * @since   JDK1.0
 */

大意如下：

该异常类标志着打开指定路径文件失败

当需要打开的文件不存在时这个异常将会被FileInputStream，FileOutputStream，RandomAccessFile的构造函数抛出

当需要打开的文件由于某些特定原因无法打开时（如尝试去用写入方式打开只读文件）也会被抛出

该类含有一个成员变量：

序列化ID：

private static final long serialVersionUID = -897856973823710492L;

含有三个方法：

默认构造方法：直接调用父类构造方法

public FileNotFoundException() {
    super();
}

构造方法：（也对应父类构造方法，把具体错误信息的字符串传递给父类

public FileNotFoundException(String s) {
    super(s);
}

构造方法：仅能被native IO方法调用（私有），传递出错的路径和错误原因

private FileNotFoundException(String path, String reason) {
    super(path + ((reason == null)//检测错误原因是否为空
                  ? ""
                  : " (" + reason + ")"));
}

这个类也十分简单，编写时遇到该异常知道错误原因即可