Re: Math.random()

From:

Lew <lew@lewscanon.com>

Newsgroups:

comp.lang.java.help

Date:

Mon, 10 Mar 2008 19:45:03 -0400

Message-ID:

<6s6dnYqAZ8qdVUjanZ2dnUVZ_vKunZ2d@comcast.com>

maya wrote:

    String[] textFileNames = directory.list(new FilenameFilter() {
      public boolean accept(File dir, String name) {
          return name.endsWith(".jpg") || name.endsWith( ".JPG");
         }
    });

    ArrayList photos = new ArrayList();

    for (int i=0; i < textFileNames.length; i++) {
      System.out.println(textFileNames[i] + " -- " + i);
      photos.add(new File(textFileNames[i]));
    }

    System.out.println("");

    Collections.shuffle(photos);
    Object _photosArr[] = photos.toArray();

The trouble with this idiom is that you create an array, *copy* it into a
List, then *copy* it back into an array. That's very wasteful. If you use
Arrays.asList() as I suggested elsethread, then you skip both the repeated
add() step and the toArray() step.

Reiterating the code fragment:
  public static File [] getImagesShuffled()
  {
    File directory = new File(System.getProperty("user.dir"));

    File [] files = directory.listFiles( new FileFilter()
      {
        public boolean accept( File file )
        {
          return file.getName().toLowerCase().endsWith(".jpg");
        }
      } );
    Collections.shuffle( Arrays.asList( files ) );
    return files;
  }

This will save both memory and execution time, a rare case when there isn't a
tradeoff between them.

You should also genericize your Collections classes when you do use them, and
make the widest appropriate type for the variable even if the object type is
narrower:

   List <File> photos = new ArrayList <File> ();

--
Lew