Lab 17: File I/O

The goal of this lab is to practice file I/O and to review designing windows.

1. Introduction

In this lab we will revisit the Sprite program from lab 15. This time we will give the program the facility to save the current state of the simulation and reload it later.

The program should work as before but with two changes:

• If the user runs the program with a filename on the command line, the program should load the configuration found in that file.
• There is a "Save" button which, if the user presses it, will bring up a window asking the user for a file name, and saving to that file.

For your convenience, the GUI and File I/O handouts (part 1, part 2) from class are available online.

If you did not complete lab15, but you are close, you might take up to about 30 minutes now to see if you can complete it. But don't take longer than that, because you'll need time for today's lab.

2. Set up

Follow these set-up instructions carefully.

Make a directory for this lab and cd into it. First, copy files from the course directory for this lab:

hg clone /cslab/class/csci235/labs/lab17
cd lab17

Then copy from your lab15 directory AddListener.java and any other class that you wrote (you should have written another action listener, perhaps named something like OkListener.java. If you previously modified either Sprite.java or Sprites.java, talk to the instructor about how to make your version work with this lab.

If you have not completed the Sprite lab, you can copy the files from /cslab/class/csci235/labs/lab17b/.

However you got the listener class files, you probably want to add them to the local Mercurial repository and commit them before you go further.

Remember that you will need to include -cp simulation.jar:. with both the javac and java commands.

3. Designing a file format

First, discuss with your partner how you can save/store a collection of Sprites. You'll need to decide on a file format, which will need to include a way to format each of the Sprites. At the end of this week's Sprite.java, you'll find a place to describe your format in a comment.

The trickiest part of this will be figuring out how to write the Color value out in a way that it can be re-constructed. One path to that is to look at the constructors for Color; you want to find a constructor for which there is a corresponding method returning the value. (Try to keep it simple. And you can rule out anything having to do with "system properties".)

You can uncomment or replace the final section in Sprite.java. You'll need something like what is there to encapsulate the conversion.

4. Writing the SaveListener

Next, finish the SaveListener class so that its actionPerformed() method puts up a window asking for a filename. (The simplest way to do this will be to provide a JTextField in which the user can type the filename. Keep it simple for now.) This window should also have a button labelled "Ok" or the equivalent.

Then write another action listener class which will close that window and do the actual saving. Be sure to catch error cases. It is OK if you print any error messages to the terminal. If you can't think of how to iterate over all of the Sprites, look here for a hint.

If you manage to write your method without looking at the hint, take a look at it now, and note especially the last paragraph.

5. Loading a saved configuration

Finally, in the file Sprites.java, find the portion of code that will load a configuration from a file and fill-in what's missing.

6. Turn in

Turn in your source files as lab17 with the command

/cslab/class/csci235/bin/handin lab17 *.java

7. Using dialogs (optional)

If you have time, here are instructions for using dialog classes to select a file and to display messages. If you want to try that, be sure that you first commit your changes to your repository before you start. Be sure you turn in what have done before you go on.