Learning Java

Files

Unless otherwise restricted, a Java application can read and write to the host filesystem with the same level of access as the user who runs the Java interpreter. Java applets and other kinds of untrusted applications can, of course, be restricted by the security policy and cut off from these services. We’ll discuss applet access at the end of this section. First, let’s take a look at the tools for basic file access.

Working with files in Java is still somewhat problematic. The host filesystem lies outside of Java’s virtual environment, in the real world, and can therefore still suffer from architecture and implementation differences. Java tries to mask some of these differences by providing information to help an application tailor itself to the local environment; we’ll mention these areas as they occur.

The java.io.File Class

The java.io.File class encapsulates access to information about a file or directory entry in the filesystem. It can be used to get attribute information about a file, list the entries in a directory, and perform basic filesystem operations like removing a file or making a directory. While the File object handles these tasks, it doesn’t provide direct access for reading and writing file data; there are specialized streams for that purpose.

File constructors

You can create an instance of File from a String pathname:

File fooFile = new File( "/tmp/foo.txt" );  
File barDir = new File( "/tmp/bar" );

You can also create a file with a relative path:

File f = ...