Question

The following codes goes through all directories and sub-directories and outputs just .java files;

import java.io.File;


public class DirectoryReader {
    private static String extension = "none";
    private static String fileName;

    public static void main(String[] args ){
        String dir = "C:/tmp";
        File aFile = new File(dir);
        ReadDirectory(aFile);
    }
    private static void ReadDirectory(File aFile) {
        File[] listOfFiles = aFile.listFiles();
        if (aFile.isDirectory()) {
             listOfFiles = aFile.listFiles();
            if(listOfFiles!=null) {
                for(int i=0; i < listOfFiles.length; i++  ) {
                    if (listOfFiles[i].isFile()) {

                        fileName = listOfFiles[i].toString();
                        int dotPos = fileName.lastIndexOf(".");
                        if (dotPos > 0) {
                            extension = fileName.substring(dotPos);
                        }                       
                        if (extension.equals(".java")) {
                        System.out.println("FILE:" + listOfFiles[i] );
                        }
                    }           
                    if(listOfFiles[i].isDirectory()) {
                        ReadDirectory(listOfFiles[i]);
                    }
                }
            }
        }
    }


}

Is this efficient? What could be done to increase the speed?

All ideas are welcome.

Answer 1

My comments:

• Possible bug: extension is not reset. Think about what happens if you ecounter file1.java and thes file2 (without a .-character?)

  Suggestion: put

  if (extension.equals(".java"))
      System.out.println("FILE:" + listOfFiles[i] );
  

  inside the body of the if (dotPos > 0)

• ReadDirectory is a method and should accourding to convention have small first letter: readDirectory

• You could clean up the code a bit by using the for-each loop:

  for(File f : listOfFiles) {
      if (f.isFile()) {
          // ...
      }           
      if(f.isDirectory()) {
          readDirectory(f);
      }
  }