IT 114: Introduction to Java

IT 114: Introduction to Java
Class 37

Topics

New Material

Restoring Library State
Helper Methods for restore_library_state
Testing restore_library_state
Refactoring Movie Methods
Improving the Library Listing
Adding Search Features
More Find Options

New Material

Restoring Library State

When restoring the library state we need to do the following

 if an archive file exits {
    construct a Scanner object on the archive file
    read in the the first line as the last_collection_no
    while there there is a next line {
        read in the the class name
        if class is Movie {
            call a method to read in lines and create a Movie object
            add it to library
        } else {
            call a method to read in lines and create a Lectures object
            add it to library
    }
}

The restore_library_state method is pretty much a direct translation into Java code of the pseudocode above

    private static void restore_library_state() throws FileNotFoundException{
        File archive_file = new File(archive_filename);
        if (archive_file.exists()) {
            Scanner input = new Scanner(archive_file);
            input.nextLine(); // skip past blank first line
            while (input.hasNextLine()){
                String class_name = input.nextLine();
                if (class_name.equals("Movie")){
                    library.add(movie_from_file(input));
                } else {
                    library.add(lectures_from_file(input));
                }
            }
        }
    }

We need to add a call to this method as the fist line on the main method

public static void main (String[] args) throws FileNotFoundException, IOException{
        restore_library_state();

Helper Methods for restore_library_state

Now we need to create the methods that do the bulk of the work in restoring the library
- movie_from_file
- lectures_from_file
In each case the code is similar to what was used to read an file to create a Movie or lectures entry

Here is movie_from_file

    private static Movie movie_from_file(Scanner input){
        int collection_no = Integer.parseInt(input.nextLine());
        String title      = input.nextLine();
        int length        = Integer.parseInt(input.nextLine());
        String format     = input.nextLine();
        String director   = input.nextLine();
        String studio     = input.nextLine();
        Movie movie       = new Movie(collection_no, title, length, format, director, studio);
        while (input.hasNextLine()){
            String line = input.nextLine();
            if (line.equals(separator)){
                break;
            }
            movie.add_actor(line);
        }
        return movie;
    }

And lectures_from_file

    private static Lectures lectures_from_file (Scanner input){
        int collection_no = Integer.parseInt(input.nextLine());
        int length        = Integer.parseInt(input.nextLine());
        String format     = input.nextLine();
        String course     = input.nextLine();
        int disc_no       = Integer.parseInt(input.nextLine());
        String instructor = input.nextLine();
        Lectures lectures = new Lectures(collection_no, length, format, course, disc_no, instructor);
        while (input.hasNextLine()){
            String line = input.nextLine();
            if (line.equals(separator)){
                break;
            }
            lectures.add_lecture(line);
        }
        return lectures;
    }

Testing restore_library_state

To test the three new methods we start with no library_archive.txt file
Then run our app to store some entries and quit

$ java VideoLibrary9
M(ovie), L(ecture), S(ee entries), D(one): m
Filename: forbidden_planet_3.txt
#1: Forbidden Planet, 98 minutes, DVD, Fred McLeod Wilcox, MGM
Walter Pidgeon
Anne Francis 
Leslie Nielson 
Warren Stevens
M(ovie), L(ecture), S(ee entries), D(one): l
Filename: ancient_civilizations_1_3.txt
#2: Origins of Great Ancient Civilizations - Disc 1, 180 minutes, DVD, Kenneth W. Harl
Cradles of Civilization
First Cities of Sumer
Mesopotamian Kings and Scribes
Hammurabi’s Babylon
Egypt in the Pyramid Age
The Middle Kingdom
M(ovie), L(ecture), S(ee entries), D(one): d
Exiting

Then we run the app again

And list what is contained in the library

$ java VideoLibrary9
M(ovie), L(ecture), S(ee entries), D(one): s
#1: Forbidden Planet, 98 minutes, DVD, Fred McLeod Wilcox, MGM
Walter Pidgeon
Anne Francis 
Leslie Nielson 
Warren Stevens
#2: Origins of Great Ancient Civilizations - Disc 1, 180 minutes, DVD, Kenneth W. Harl
Cradles of Civilization
First Cities of Sumer
Mesopotamian Kings and Scribes
Hammurabi’s Babylon
Egypt in the Pyramid Age
The Middle Kingdom
M(ovie), L(ecture), S(ee entries), D(one): d
Exiting

Refactoring Movie Methods

The methods add_movie and movie_from_file have much code in common

    private static Movie add_movie(Scanner console)throws FileNotFoundException{
        System.out.print("Filename: ");
        String filename   = console.next();
        File file         = new File(filename);
        Scanner input     = new Scanner(file);
        int collection_no = get_collection_no();
        String title      = input.nextLine();
        int length        = Integer.parseInt(input.nextLine());
        String format     = input.nextLine();
        String director   = input.nextLine();
        String studio     = input.nextLine();
        Movie movie       = new Movie(collection_no, title, length, format, director, studio);
        while (input.hasNextLine()){
            movie.add_actor(input.nextLine());
        }
        System.out.println(movie);
        return movie;
    }

    private static Movie movie_from_file(Scanner input){
        int collection_no = get_collection_no();
        String title      = input.nextLine();
        int length        = Integer.parseInt(input.nextLine());
        String format     = input.nextLine();
        String director   = input.nextLine();
        String studio     = input.nextLine();
        Movie movie       = new Movie(collection_no, title, length, format, director, studio);
        while (input.hasNextLine()){
            String line = input.nextLine();
            if (line.equals(separator)){
                break;
            }
            movie.add_actor(line);
        }
        return movie;
    }

This is not good
If we ever decided to change something in the Movie class we would have to change the code in both methods
We need to refactor the code to eliminate this duplication
The red area are the same
And the bodies of the while loop are similar
movie_from_file has to check for the separator
But this text will never occur in the file used to add an entry
So adding the test for separator will not affect the add method
The only real difference is printing the Movie object
But we can leave that to the calling method
Thinking this way, we can just have add_movie call movie_from_file
After it has created the Scanner object
So we will keep movie_from_file as it is

And change add_movie

    private static Movie add_movie(Scanner console)throws FileNotFoundException{
        System.out.print("Filename: ");
        String filename   = console.next();
        File file         = new File(filename);
        Scanner input     = new Scanner(file);
        Movie movie       = movie_from_file(input);
        System.out.println(movie);
        return movie;
    }

With Lectures we have a similar situation

    private static Lectures add_lectures(Scanner console)throws FileNotFoundException{
        System.out.print("Filename: ");
        String filename   = console.next();
        File file         = new File(filename);
        Scanner input     = new Scanner(file);
        int collection_no = get_collection_no();
        int length        = Integer.parseInt(input.nextLine());
        String format     = input.nextLine();
        String course     = input.nextLine();
        int disc_no       = Integer.parseInt(input.nextLine());
        String instructor = input.nextLine();
        Lectures lectures = new Lectures(collection_no, length, format, course, disc_no, instructor);
        while (input.hasNextLine()){
            lectures.add_lecture(input.nextLine());
        }
        System.out.println(lectures);
        return lectures;
    }

    private static Lectures lectures_from_file (Scanner input){
        int collection_no = get_collection_no();
        int length        = Integer.parseInt(input.nextLine());
        String format     = input.nextLine();
        String course     = input.nextLine();
        int disc_no       = Integer.parseInt(input.nextLine());
        String instructor = input.nextLine();
        Lectures lectures = new Lectures(collection_no, length, format, course, disc_no, instructor);
        while (input.hasNextLine()){
            String line = input.nextLine();
            if (line.equals(separator)){
                break;
            }
            lectures.add_lecture(line);
        }
        rreturn lectures;
    }

We can do the same thing with

Improving the Library Listing

The reason you catalog anything is to make it easy to find something again
So we need to build a search feature into our app
But before we do this we should change the output of the listing function

Currently the output of this function is several lines long

$ java VideoLibrary10
M(ovie), L(ecture), S(ee entries), D(one): s
#1: Forbidden Planet, 98 minutes, DVD, Fred McLeod Wilcox, MGM
Walter Pidgeon
Anne Francis 
Leslie Nielson 
Warren Stevens
#2: Origins of Great Ancient Civilizations - Disc 1, 180 minutes, DVD, Kenneth W. Harl
Cradles of Civilization
First Cities of Sumer
Mesopotamian Kings and Scribes
Hammurabi’s Babylon
Egypt in the Pyramid Age
The Middle Kingdom
#3: The Day the Earth Stood Still, 92 minutes, DVD, Robert Wise, 20th Century Fox
Michael Rennie
Patricia Neal
Hugh Marlowe
M(ovie), L(ecture), S(ee entries), D(one): d
Exiting

As the library grows, this output would become annoyingly long
To improve things we will make some changes in Video
And the Movie and Lectures classes which extend it
In Video we will keep toString the same
But will add a new method short_string
We need to create this method even though inside Video it will only call its own toString method
Both Movie and Lectures will override this method to create a string that will only take up one line

Here are the changes in Video

    public String toString(){
        return "#" + collection_no + ": " + title + ", " + length 
            + " minutes, " + format;
    }

    public String short_string(){
        return toString();
    }

These are the changes in Movie

    public String toString(){
        String value = short_string();
        for (int i = 0; i < actors.size(); i++){
            value += "\n" + actors.get(i) ;
        }
        return value;
    }

    public String short_string(){
        return super.toString() + ", " + director + ", " + studio;
    }

And for Lectures

    public String toString() {
        String value =  short_string();
        for (int i = 0; i < lectures.size(); i++){
            value += "\n" + lectures.get(i) ;
        }
        return value; 
    }
    public String short_string() {
        return super.toString() + instructor;
    }}

Now we need to change list_videos to use the new short_string method

    private static void list_videos(){
        for (int i = 0; i < library.size(); i++){
            Video entry = library.get(i);
            System.out.println(entry.short_string());
        }
    }

Now when we list the collection we get

$ java VideoLibrary11
M(ovie), L(ecture), S(ee entries), D(one): s
#1: Forbidden Planet, 98 minutes, DVD, Fred McLeod Wilcox, MGM
#2: Origins of Great Ancient Civilizations - Disc 1, 180 minutes, DVD, Kenneth W. Harl
#3: The Day the Earth Stood Still, 92 minutes, DVD, Robert Wise, 20th Century Fox
#4: Origins of Great Ancient Civilizations - Disc 2, 180 minutes, DVD, Kenneth W. Harl
M(ovie), L(ecture), S(ee entries), D(one): d
Exiting

Adding Search Features

Now we will some search features

In order to do this we will need to add a new "Find" option to the menu

    private static final String prompt  = "M(ovie), L(ecture), S(ee entries), F(ind), D(one): ";

And a new option in the while loop of the main method

} else if (action.equals("f")) {
                find_videos(console);
            }

find prints its own menus using the new constant find_prompt

    private static final String find_prompt        = "M(ovies), L(ectures): ";

Then it calls videos_for_class to print the proper entries

    private static void find_videos(Scanner console){
        System.out.print(find_prompt);
        String action = console.next();
        action        = action.trim();        // remove any leading or trailing whitespace
        action        = action.toLowerCase(); // only lowercase letters
        if (action.equals("m")) {
            videos_for_class("Movie");
        } else if (action.equals("l")) {
            videos_for_class("Lectures");
        } else {
            System.out.println(action + " is not a valid choice");
        }
    }

    private static void videos_for_class(String class_name){
        for (int i = 0; i < library.size(); i++){
            Video entry = library.get(i);
            String entry_class_name = entry.getClass().getSimpleName();
            if (entry_class_name.equals(class_name)){
                System.out.println(entry);
                System.out.println(separator);
            }
        }
    }

$ jv VideoLibrary12.java 
M(ovie), L(ecture), S(ee entries), F(ind), D(one): f
M(ovies), L(ectures): m
#1: Forbidden Planet, 98 minutes, DVD, Fred McLeod Wilcox, MGM
Walter Pidgeon
Anne Francis 
Leslie Nielson 
Warren Stevens
----------------------------------------
#3: The Day the Earth Stood Still, 92 minutes, DVD, Robert Wise, 20th Century Fox
Michael Rennie
Patricia Neal
Hugh Marlowe
----------------------------------------
M(ovie), L(ecture), S(ee entries), F(ind), D(one): f
M(ovies), L(ectures): l
#2: Origins of Great Ancient Civilizations - Disc 1, 180 minutes, DVD, Kenneth W. Harl
Cradles of Civilization
First Cities of Sumer
Mesopotamian Kings and Scribes
Hammurabi’s Babylon
Egypt in the Pyramid Age
The Middle Kingdom
----------------------------------------
#4: Origins of Great Ancient Civilizations - Disc 2, 180 minutes, DVD, Kenneth W. Harl
Imperial Egypt
New Peoples of the Bronze Age
The Collapse of the Bronze Age
From Hebrews to Jews
Imperial Assyria
The Persian Empire
----------------------------------------
M(ovie), L(ecture), S(ee entries), F(ind), D(one): d
Exiting

More Find Options

Let's add two more find options that look for fields specific to different video types
- Director
- Instructor

First we have to add these to the find_prompt

    private static final String find_prompt  = "M(ovies), L(ectures, D(irectors), I(instructors): ";

To find either director or instructor find_videos, we need a search value
We will create the helper method get_search_value to do this
Then it need another helper method videos_for_field to actually find the proper entries

Here is the new version of find_videos

    private static void find_videos(Scanner console){
        String search_value;
        System.out.print(find_prompt);
        String action = console.next();
        action        = action.trim();        // remove any leading or trailing whitespace
        action        = action.toLowerCase(); // only lowercase letters
        if (action.equals("m")) {
            videos_for_class("Movie");
        } else if (action.equals("l")) {
            videos_for_class("Lectures");
        } else if (action.equals("d")) {
            search_value = get_search_value(console, "Movie", "director");
            videos_for_field("Movie", "director", search_value);
        } else if (action.equals("i")) {
            search_value = get_search_value(console, "Lectures", "instructor");
            videos_for_field("Lectures", "instructor", search_value);
        } else {
            System.out.println(action + " is not a valid choice");
        }
    }

And here are the helper methods

    private static String get_search_value(Scanner console, String class_name, String field_name){
        System.out.print(field_name + " value: ");
        String serach_value = console.next();
        serach_value = serach_value.trim();
        return serach_value.toLowerCase(); 
    }

    private static void videos_for_field(String class_name, String field_name, String search_value){
        String list = "";
        String field_value;
        for (int i = 0; i < library.size(); i++){
            Video entry = library.get(i);
            String entry_class_name = entry.getClass().getSimpleName();
            if (entry_class_name.equals(class_name)){
                if (class_name.equals("Movie")) {
                    Movie movie = (Movie) entry;
                    field_value = movie.director().toLowerCase();
                    if (field_value.contains(search_value)) {
                        list += entry.toString() + "\n" + separator + "\n";
                    }
                } else if (class_name.equals("Lectures")) {
                    Lectures lectures = (Lectures) entry;
                    field_value = lectures.instructor().toLowerCase();
                    if (field_value.contains(search_value)) {
                        list += entry.toString() + "\n" + separator + "\n";
                    }
                }
            }
        }
        if (list.length() > 0) {
            System.out.println(list);
        } else {
            System.out.println("Could not find " + field_name + " matching " + search_value);
        }
    }

Running the app we get

$ java VideoLibrary13 
M(ovie), L(ecture), S(ee entries), F(ind), D(one): f
M(ovies), L(ectures, D(irectors), I(instructors): d
director value: adfafd
Could not find director matching adfafd
M(ovie), L(ecture), S(ee entries), F(ind), D(one): f
M(ovies), L(ectures, D(irectors), I(instructors): d
director value: wilcox
#1: Forbidden Planet, 98 minutes, DVD, Fred McLeod Wilcox, MGM
Walter Pidgeon
Anne Francis 
Leslie Nielson 
Warren Stevens
----------------------------------------

M(ovie), L(ecture), S(ee entries), F(ind), D(one): f
M(ovies), L(ectures, D(irectors), I(instructors): i
instructor value: harl
#3: Origins of Great Ancient Civilizations - Disc 1, 180 minutes, DVD, Kenneth W. Harl
Cradles of Civilization
First Cities of Sumer
Mesopotamian Kings and Scribes
Hammurabi’s Babylon
Egypt in the Pyramid Age
The Middle Kingdom
----------------------------------------
#4: Origins of Great Ancient Civilizations - Disc 2, 180 minutes, DVD, Kenneth W. Harl
Imperial Egypt
New Peoples of the Bronze Age
The Collapse of the Bronze Age
From Hebrews to Jews
Imperial Assyria
The Persian Empire
----------------------------------------

M(ovie), L(ecture), S(ee entries), F(ind), D(one): d
Exiting