Directory and Filesystem Operations - Java - page 453

The FilenameFilter need not be a separate class; case in point, the online code example
FNFilter2 implements the interface directly in the main class, resulting in a slightly shorter
file. An anonymous inner class could be used. The example FNFilterL shows it as a lambda
expression, which is shorter still:

dir_file/FNFilterL.java

// Generate the selective list, with a Lambda Expression
String [] dirs = new new java . io . File ( dirName ). list (

( dir , s ) -> {
return

return s . endsWith ( ".java" ) ||
s . endsWith ( ".class" ) ||
s . endsWith ( ".jar" );

}

);
Arrays . sort ( dirs ); // Sort it (see Data Structuring chapter))

for for ( String d : dirs ) {

System . out . println ( d ); // Print the list

}

In a full-scale application, the list of files returned by the FilenameFilter would be chosen
dynamically, possibly automatically, based on what you were working on. As we'll see in
Choosing a File with JFileChooser , the file chooser dialogs implement a superset of this
functionality, allowing the user to select interactively from one of several sets of files to be
listed. This is a great convenience in finding files, just as it is here in reducing the number of
files that must be examined.

Getting the Directory Roots

Problem

You want to know about the top-level directories, such as C:\ and D:\ on Windows.

Solution

Use the static method File.listRoots() .