Directory and Filesystem Operations - Java - page 452

this, and I found it quite useful. By using listFiles() , which constructs a new File object
for each name, you could print the size of each, as per the DOS dir command or the Unix ls -
l command (see Getting File Information ) . Or you could figure out whether each is a file, a
directory, or neither. Having done that, you could pass each directory to your top-level func-
tion, and you'd have directory recursion (the Unix find command, or ls -R , or the DOS DIR
/S command).

A more flexible way to list filesystem entries is with list(FilenameFilter ff) . File-
nameFilter is a little interface with only one method: boolean accept(File inDir ,
String fileName) . Suppose you want a listing of only Java-related files ( *.java , *.class ,
*.jar , etc.). Just write the accept() method so that it returns true for these files and false for
any others. Here is the Ls class warmed over to use a FilenameFilter instance (my
OnlyJava class implements this interface) to restrict the listing:

public public class class FNFilter FNFilter {

public public static static void void main ( String argh_my_aching_fingers []) {

// Generate the selective list, with a one-use File object.
String [] dirs = new new java . io . File ( "." ). list ( new new OnlyJava ());

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

for for ( String d : dirs ) {

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

}

}

/** This class implements the FilenameFilter interface.
* The Accept method returns true for .java, .class and .jar files.
*/
private private static static class class OnlyJava OnlyJava implements implements FilenameFilter {

public public boolean boolean accept ( File dir , String s ) {

iif ( s . endsWith ( ".java" ) ||
s . endsWith ( ".class" ) ||
s . endsWith ( ".jar" )) {

return return true true ;

}
// others: projects, ... ?
return return false false ;

}

}

}