Java in a Nutshell, 5th Edition

Files and Directories

The java.io.File class represents a file or a directory and defines a number of important methods for manipulating files and directories. Note, however, that none of these methods allow you to read the contents of a file; that is the job of java.io.FileInputStream , which is just one of the many types of I/O streams used in Java and discussed in the next section. Here are some things you can do with File:

import java.io.*;
import java.util.*;

// Get the name of the user's home directory and represent it with a File
File homedir = new File(System.getProperty("user.home"));
// Create a File object to represent a file in that directory
File f = new File(homedir, ".configfile");

// Find out how big a file is and when it was last modified
long filelength = f.length();
Date lastModified = new java.util.Date(f.lastModified());

// If the file exists, is not a directory, and is readable, 
// move it into a newly created directory.
if (f.exists() && f.isFile() && f.canRead()) {       // Check config file
  File configdir = new File(homedir, ".configdir"); // A new config directory
  configdir.mkdir();                                // Create that directory
  f.renameTo(new File(configdir, ".config"));       // Move the file into it
}

// List all files in the home directory
String[] allfiles = homedir.list();

// List all files that have a ".java" suffix
String[] sourcecode = homedir.list(new FilenameFilter() {
  public boolean accept(File d, String name) { return name.endsWith(".java"); }
});

The File class gained ...