Exercise

Write an application that stores and uses persistent data.

Objectives

• Discover how to store data for an application.
• Discover how to create objects that can persist.
• Discover how to save and retrieve data.

Setup

1. Extract music_stores_incomplete.zip
2. In the IDE, open the music_stores.jdw workspace
3. Open the MusicStores.java source file.

Tasks

1. In the static initializer, retrieve a reference to a PersistentObject using the store variable.
2. In the synchronized block, if the PersistentObject is empty, set its contents to a new Vector.
3. Retrieve PersistentObject contents and store it in a Vector.
   TIP: Use the _data variable already defined.
4. Add code to the StoreInfo inner class to define an object that can persist. TIP: Each object stores information about one music store.
5. Add code to saveItem to create a Save menu item that saves the music store information that users have entered.
6. Add code to getItem to create a Get menu item that retrieves and displays data from the last music store that was added.

Check Your Work

(from music_store_complete.zip)

Review

In this exercise, you discovered the following things:

• how to create a data storage area for an application
• how to create a new type of object that can persist
• how to retrieve data from a persistent data store
• how to add data to a persistent data store