The java.io.File class contains methods like list() or listFiles() that will return the list of a file as an array of String or File objects.

You can create a class that implements the java.io.FilenameFilter interface. The only method you have to implement is accept() where you define which are the filenames you want to include in your listing. For example you can accept all the files that have the jgp, png or gif extension.

Once you have that class, you can pass it to the list() or listFiles() methods, and you will get the array with all the images files in your dir.