Java.io.File类在Java中的应用

File类是Java对文件或目录路径名的表示。因为文件和目录名在不同的平台上有不同的格式，一个简单的字符串不足以命名它们。文件类包含几个方法，用于处理路径名、删除和重命名文件、创建新目录、列出目录的内容，以及确定文件和目录的几个常见属性。

如何创建一个文件对象 ？

一个文件对象的创建是通过传入一个代表文件名称的字符串、一个字符串或另一个文件对象。比如说

File a = new File("/usr/local/bin/geeks");

这为/usr/local/bin目录下的geek文件定义了一个抽象的文件名。这是一个绝对的抽象文件名。

文件类的构造函数

文件类的方法

例1： 检查一个文件或目录是否实际存在的程序。

// In this Java program, we accepts a file or directory name from// command line arguments. Then the program will check if// that file or directory physically exist or not and// it displays the property of that file or directory.  import java.io.File;  // Displaying file propertyclass fileProperty {    public static void main(String[] args)    {          // accept file name or directory name through        // command line args        String fname = args[0];          // pass the filename or directory name to File        // object        File f = new File(fname);          // apply File class methods on File object        System.out.println("File name :" + f.getName());        System.out.println("Path: " + f.getPath());        System.out.println("Absolute path:"                           + f.getAbsolutePath());        System.out.println("Parent:" + f.getParent());        System.out.println("Exists :" + f.exists());          if (f.exists()) {            System.out.println("Is writable:"                               + f.canWrite());            System.out.println("Is readable" + f.canRead());            System.out.println("Is a directory:"                               + f.isDirectory());            System.out.println("File Size in bytes "                               + f.length());        }    }}

输出

File name :file.txtPath: file.txtAbsolute path:C:\Users\akki\IdeaProjects\codewriting\src\file.txtParent:nullExists :trueIs writable:trueIs readabletrueIs a directory:falseFile Size in bytes 20

例2： 显示一个目录的所有内容的程序

这里我们将从键盘上接受一个目录名称，然后显示该目录的所有内容。为了这个目的，可以使用list()方法。

String arr[]=f.list();

在前面的语句中，list()方法使所有的目录条目被复制到数组 arr[]中。然后将这些数组元素arr[i]传递给File对象，并测试它们以了解它们是否代表一个文件或目录。

// Java Program to display all // the contents of a directoryimport java.io.BufferedReader;import java.io.File;import java.io.IOException;import java.io.InputStreamReader;  // Displaying the contents of a directoryclass Contents {    public static void main(String[] args)        throws IOException    {        // enter the path and dirname from keyboard        BufferedReader br = new BufferedReader(            new InputStreamReader(System.in));          System.out.println("Enter dirpath:");        String dirpath = br.readLine();        System.out.println("Enter the dirname");        String dname = br.readLine();          // create File object with dirpath and dname        File f = new File(dirpath, dname);          // if directory exists,then        if (f.exists()) {            // get the contents into arr[]            // now arr[i] represent either a File or            // Directory            String arr[] = f.list();              // find no. of entries in the directory            int n = arr.length;              // displaying the entries            for (int i = 0; i < n; i++) {                System.out.println(arr[i]);                // create File object with the entry and                // test if it is a file or directory                File f1 = new File(arr[i]);                if (f1.isFile())                    System.out.println(": is a file");                if (f1.isDirectory())                    System.out.println(": is a directory");            }            System.out.println(                "No of entries in this directory " + n);        }        else            System.out.println("Directory not found");    }}

输出

Enter dirpath:C:\Users\akki\IdeaProjects\Enter the dirnamecodewriting.idea: is a directoryan1.txt: is a filecodewriting.iml: is a filefile.txt: is a fileout: is a directorysrc: is a directorytext: is a fileNo of entries in this directory 7