对Java正则表达式感到困惑

Question

What I'm trying to do is look from a list of files in a directory and see which file name has the pattern 'output'. If the file does contain the word 'output' then I just want to print it to screen. That's it.

Here is my code that doesn't work. Why doesn't it work?

package duplicate_search;

import java.io.File;
import java.util.regex.*;
import java.util.Scanner;

public class Search {
public static void main(String [] args){
    Scanner keyboard = new Scanner(System.in);
    System.out.println("Enter the directory to search: ");
    String dir = keyboard.next();

    Pattern p = Pattern.compile("output");
    Matcher m = null;
    System.out.println
              ("Now search for *." + p + " files.");
    File folder = new File(dir);
    File[] listOfFiles = folder.listFiles();


    for(File f : listOfFiles){
        m = p.matcher(f.getName());
        if(m.matches()){
            System.out.println(f.getName());
        }
      }
    }
}

Answer 1

If you want to match filenames that contain "output", then you don't want to use matches , but instead, find .

From the docs:

The matches method attempts to match the entire input sequence against the pattern.

http://docs.oracle.com/javase/1.5.0/docs/api/java/util/regex/Matcher.html

Answer 2

.matches() does a full match. check for .*output.* or use find()

Answer 3

Why aren't you using contains() method? Unless I'm not getting your question right you can check if a string contains that character sequence:

f.getName().contains("output"); //Returns true if the string contains "output"

IMHO a regular expression seems like an overkill here, unless you have your reasons of course.

Answer 4

Here is the modified code,

import java.io.File;
import java.util.regex.*;
import java.util.Scanner;

public class Search {
public static void main(String [] args){
    Scanner keyboard = new Scanner(System.in);
    System.out.println("Enter the directory to search: ");
    String dir = keyboard.next();

    Pattern p = Pattern.compile("output");
    Matcher m = null;
    System.out.println
              ("Now search for *." + p + " files.");
    File folder = new File(dir);
    File[] listOfFiles = folder.listFiles();


    for(File f : listOfFiles){
        m = p.matcher(f.getName());
        if(m.find()){ // change to find instead of m.matches()
            System.out.println(m.group()); // return the string sequence which is matched
        }
      }
    }
}