Java Cookbook

Getting File Information

Problem

You need to know all you can about a given file on disk.

Solution

Use a java.io.File object.

Discussion

The File class has a number of “informational” methods. To use any of these, you must construct a File object containing the name of the file it is to operate upon. It should be noted up front that creating aFileobject has no effect on the permanent filesystem; it is only an object in Java’s memory. You must call methods on the File object in order to change the filesystem; as we’ll see, there are numerous “change” methods, such as one for creating a new (but empty) file, one for renaming a file, etc., as well as many informational methods. Table 10-1 lists some of the informational methods.

Table 10-1. java.io.File methods

Return type	Method name	Meaning
boolean	exists( )	True if something of that name exists
String	getCanonicalPath( )	Full name
String	getName( )	Relative filename
String	getParent( )	Parent directory
boolean	canRead( )	True if file is readable
boolean	canWrite( )	True if file is writable
long	lastModified( )	File modification time
long	length( )	File size
boolean	isFile( )	True if it’s a file
boolean	isDirectory( )	True if it’s a directory (Note: it might be neither)

You can’t change the name stored in a File object; you simply create a new File object each time you need to refer to a different file.

import java.io.*; import java.util.*; /** * Report on a file's ...