Using FileName Filter is an Advantage ?

Question

Hi all,
Assume there are two versions of program , let me tell you the objective of the program.
Objective : To list the directory and select the files based on the given criteria.
Version 1:
Step 1: get the files list by using File.listFiles()
Step 2. Loop through the list and select the files based on the criteria.
Step 3: Process the selected files.
Version 2:
Step 1 : Get the files using File.listFiles(Filter)(embed the selection criteria inside the filter class).
Step 2 : Process the selected files.
My assumption is Version 2 will run faster than Version 1:
Guys could you please tell me whether my assumption is right ?

Answer 1

There's no reason to think the Filter method will run any faster. In fact, it might be a tiny, imperceptible bit slower, since it will probably have an extra level of method calling. Note that this theoretical minuscule speed difference is NOT a reason to choose one over the other.
The reason to use the Filter method is for encapsulation and separation of responsibility. The Filter is a way to encapsulate the selection criteria, and confine that responsibility to a class whose job is precisely that. This lets you change which files you'll process without changing the processing loop. The filter can come from somewhere completely separate from the processing loop.
For example:
public class FileUtil {
  public static getSumOfFileSizes(File directory, FileNameFilter filter) {
    File[] files = directory.listFiles(filter);
    long size = 0L;
    for (File file : files) {
      size += file.length();
    return size;
}Now if I want to know the total sizes of all the .jpg files and all the .gif files in the directory, I just do
long jpgSizes = FileUtil.getSumOfFileSizes(directory, new FileNameFilter() {
  public boolean accept(File directory, String name) {
    return name.endsWith(".jpg");
long gifSizes = FileUtil.getSumOfFileSizes(directory, new FileNameFilter() {
  public boolean accept(File directory, String name) {
    return name.endsWith(".gif");
  }});Note that I only write the size summing code once, and I never change it. I could of course define a FileFilter, say EndsWithFileFilter that I just pass the extension to look for, rather than have those separate anonymous inner classes. The point is that the processing code is completely independent of the file selection code.