Programming Tutorials

FilenameFilter - sample program in Java

By: Reema sen Printer Friendly Format    

You will often want to limit the number of files returned by the list() method to include only those files that match a certain filename pattern, or filter. To do this, you must use a second form of list(), shown here:

String[ ] list(FilenameFilter FFObj)

In this form, FFObj is an object of a class that implements the FilenameFilter interface. FilenameFilter defines only a single method, accept(), which is called once for each file in a list. Its general form is given here:

boolean accept(File directory, String filename)

The accept( ) method returns true for files in the directory specified by directory that should be included in the list (that is, those that match the filename argument), and returns false for those files that should be excluded.

The OnlyExt class, shown next, implements FilenameFilter. It will be used to modify the preceding program so that it restricts the visibility of the filenames returned by list( ) to files with names that end in the file extension specified when the object is constructed.

import java.io.*;
public class OnlyExt implements FilenameFilter {
String ext;
public OnlyExt(String ext) {
this.ext = "." + ext;
}
public boolean accept(File dir, String name) {
return name.endsWith(ext);
}
}

The following program will only display files that use the .html extension.

// Directory of .HTML files.
import java.io.*;
class DirListOnly {
public static void main(String args[]) {
String dirname = "/java";
File f1 = new File(dirname);
FilenameFilter only = new OnlyExt("html");
String s[] = f1.list(only);
for (int i=0; i < s.length; i++) {
System.out.println(s[i]);
}
}
}

This tutorial is an extract from the "The Complete Reference Part 2 by Herbert Schildt".