You are developing software for a computer file system. The system has
several kinds of files (e.g. Word documents and video clips). Every file
has a name. Each kind of file has a distinctive action that's taken when
it is opened. A client can ask to redisplay a file; for most kinds of
files, this does nothing, but some kinds of files may do something
interesting. 

Declare and implement the classes named in the sample program below in
such a way that the program compiles, executes, and produces exactly the
output shown. (A real implementation would actually play videos and show
pictures, but for now we'll stick to simple text output.) Do not change
the implementations of main and openAndRedisplay.

        public class FileExample
        {
            public static void main(String[] args)
            {
                File[] files = new File[4];
                files[0] = new WordDoc("script.doc");
                  // Videos have a name and running time
                files[1] = new Video("trailer.mpg", 57);
                files[2] = new Picture("radcliffe.jpg");
                files[3] = new Picture("watson.jpg");
        
                for (int k = 0; k < files.length; k++)
                    openAndRedisplay(files[k]);
            }
        
            public static void openAndRedisplay(File f)
            {
                System.out.println(f.getName() + ": " + f.open());
                System.out.print("Redisplay: ");
                f.redisplay();
                System.out.println();
            }
        }

	// You declare File, WordDoc, Video, and Picture

Your declarations of those classes must be such that the code above will
produce this output:

        script.doc: open Word document
        Redisplay: 
        trailer.mpg: play 57 second video
        Redisplay: replay video
        radcliffe.jpg: show picture
        Redisplay: 
        watson.jpg: show picture
        Redisplay: