Homework 7
Grouping More Objects

Overview - The purpose of the homework is to practice grouping objects using ArrayList and HashMap. An Album class that groups and displays digital images to create various slide shows will be implemented. The Album will display selected images using a provided PictureViewer class. A simple, graphical user interface to the Album is provided by the AlbumSkin class.

Problem description - An album groups images. The images consist of two parts:

1. name - The name of the image, a String.
2. filename - The name of the image file, a String.

For example, the name "Fish" associates an image stored as filename "Fishing.jpg".

For this assignment, an Album is a grouping of an arbitrary number of images and the methods to:

1. create a group of images,
2. display the group, either sequentially or in random order,
3. and to print the name and filename of the images in the group.

The album will use an ArrayList to group image names; a HashMap will group image filenames as in the figure at right.

• An ArrayList  is useful to group objects by associating an integer index with an object. For example, the figure at right associates an integer index 0, 1 or 2 with name of an image in the album.
• A HashMap is useful to group objects by associating an arbitrary key with an object. For example, the figure at right associates the name of an image in the album with a filename.

 

Example using the ArrayList to locate the HashMap filename

Consider an ArrayList named aL and a HashMap hM with the following values:

ArrayList  aL   0 Title 1 Outback 2 Fish

HashMap  hM   Fish Fishing.jpg Title Title.jpg Outback Outback.jpg

The values aL are the keys of hM.

aL.get(1) is "Outback" hM.get("Outback") is "Outback.jpg" hM.get( aL.get( 1 ) ) is "Outback.jpg"

Accessing all the values of an ArrayList is simple because we know the indices must be 0, 1, 2, ....

To print aL values "Title", "Outback" and "Fish":

for ( int i=0; i< aL.size(); i++)      System.out.println( aL.get( i ) );

Accessing all the values of a HashMap is more difficult because the keys could be any String: "Title", "Ray", "*&%".

But we've defined aL to hold the keys of hM, then the HashMap values can be accessed by hM.get( aL.get( i ) ).

To print all hM values "Title.jpg, "Outback.jpg" and "Fishing.jpg":

for ( int i=0; i< aL.size(); i++)      System.out.println( hM.get( aL.get( i ) ) );

 

We will organize the photo album by:

• placing friendly names in an ArrayList which is simple to access by index.
• placing photo filenames in a HashMap which is simple to associate the friendly name with the filename.

To display a photo number 2, the friendly name at index 2 "Outback" is the HashMap key associated with the filename "Outback.jpg".

aL.get(2) is "Outback" hM.get("Outback") is "Outback.jpg" hM.get( aL.get( 2 ) ) is "Outback.jpg"

 

Getting started

• Download and run the HW7.exe file to extract the initial project files. Unzip to folder HW7 in your BlueJ directory (normally C:\Users\username\bluej\HW7).
   
  1. Open the HW7 project. The class view should appear as at right.
      
  2. Test by creating a PictureViewer object. Use picture parameter "Fishing.jpg" and delay parameter of 6.

  The PictureViewer has a single constructor with parameters of picture (the String filename to view) and delay (the time delay in seconds during which the image is viewed).
   

Assignment

Album class

1. Create a new class named Album.
    
2. To use ArrayList, Random, HashMap and Iterator classes, add the first lines of Album exactly as:

   import java.util.HashMap; import java.util.ArrayList; import java.util.Iterator; import java.util.Random;

3. Add fields.
   • Add one ArrayList field. This will hold the names of the images as Strings.
   • Add one HashMap field. The keys are the image names and the values the image filenames. Key and value are String type.
      
4. Add a Album constructor that initializes the ArrayList and HashMap fields.
    
5. Add a mutator method addImage that adds an image. The addImage method has two String parameters: the name and filename of the image.
   1. The name is stored in the ArrayList.
   2. The name is the HashMap key and filename is the corresponding HashMap value.

   Test by:

   • Create an Album object.
   • Add two images (name: "fish", fileName: "fishing.jpg" and name: "outback", fileName: "outback.gif") using addImage.
   • Inspect the Album object, follow the arrows for the HashMap and ArrayList until you see the "fish".
      
6. To speed up the testing process we'll automate of adding images. Add the following mutator method createImages that adds images to the album; you can copy and paste.

   public void createImages() {     addImage("Fish", "Fishing.jpg");     addImage("Dive", "Dive.jpg");     addImage("Rocking","Rocking.jpg");     addImage("Local Color","local.jpg");     addImage("Outback","Outback.gif"); }

   • Test by creating an Album instance and calling the createImages method.
   • Inspect the Album instance and follow the arrows on the ArrayList until you find the names of the images.
   • Add a call to createImages() at the end of the Album constructor to automatically initialize an Album for testing.
      
7. Add an accessor method getSize that returns the size of the album, the size of the ArrayList.
   • Test by:
     • Create a Album instance
     • Call the getSize method.
       
8. Add an accessor method getName to return the name at the ArrayList index specified in the method parameter. The method has one int  parameter.
   • Test by:
     • Create a Album instance
     • Call the getName(2) method.
        
9. Add an accessor method getFileName to return the filename corresponding a name in the HashMap specified in the method parameter. The method has one String  parameter.
   • Test by:
     • Create a Album instance
     • Call the getFileName("Fish") method. It should return the filename "Fishing.jpg".
        
10. Add the method view to view a single image. The method has one String parameter, the name of the image (not the filename) to view. Recall that the name is a HashMap key identifying the filename to view.
    • Use getFileName() to get filename; getFileName("Fish") returns "Fishing.jpg" as the filename.
    • Use the PictureViewer constructor to view the image filename. The following views "Fishing.jpg" for 4 seconds.
      • new PictureViewer( "Fishing.jpg", 4);
    • Test by:
      • Create an Album instance
      • Call the view("Fish") method to view the "Fishing.jpg" file.
         
11. Add a printAlbum method to print the name and filename of all images in the album to the terminal window.
    • Recall that the name is in the ArrayList, the getSize() method returns the number of images in the Album.
    • Use getFileName() to get filename; recall that getFileName("Fish") returns "Fishing.jpg" as the filename.
    • Test by:
      • Create an Album instance.
      • Call the printAlbum method. The results should appear similar to:
         

        <Fish, Fishing.jpg> <Dive, Dive.jpg> <Rocking, Rocking.jpg> <Local Color, local.jpg> <Outback, Outback.gif>

         

12. Add a viewAlbum method to view all images in the album.
    • Recall that the name is in the ArrayList.
    • Use view(name) to view an image.
    • Test by:
      • Create an Album instance
      • Call the viewAlbum method.
      • All the Album images should be displayed.
         
13. Add a randomViewAlbum method to randomly view a given number of images in the album. The method has one int parameter, the number of images to randomly view.
    • Use the Random class method nextInt() to generate a random integer; you will need a random number between 0 and the size of the album, remember your getSize() method.
    • Recall that the name is in the ArrayList and filename is in the HashMap; use view(name) to view an image.
    • Test by:
      • Create an Album instance
      • Call the randomViewAlbum(10) method to randomly view 10 images.
         
14. Add a basic skin graphical interface for your Album.
    • Test by:
      • Create a AlbumSkin object.
      • Click on an image name in the AlbumSkin window to view the image.
         
15. Add some of your photos
    • Copy JPG or GIF files to the HW7 directory. Other formats might work also.
    • Modify the createImages() method to use your photos.
    • Test by:
      • Create a AlbumSkin object.
      • Click on an image name in the AlbumSkin window to view one of your images.
      • Capture the AlbumSkin window (Alt Prnt Scrn) and paste into Word.

Turn in

C201 OnCourse Dropbox - Create a HW7 folder in the C201 OnCourse DropBox. Copy the following:

1. Album JAVA file.
2. A Word file with Screen shot of AlbumSkin with one of your images. Use Alt Prnt Scrn to capture the window, then paste into Word.