Interface H5: Classes and Adapters
CSE 335, Spring 2009
Due by Tuesday, March 3 at 11:59 p.m.
Objectives
1. Exercise use of abstract classes and interfaces. 2. Understand reasons for refactoring a set of classes in order to support maintenance goals. 3. Apply the adapter and observer patterns.
Description
The files in /user/cse335/S09/H5-src/ comprise a small GUI application that allows users to enter an unsigned integer in some interval [lower bound . . . upper bound]. The GUI itself contains a text-entry box, into which the user may type the integer, and a reset button. The text-entry box ensures that any input is valid and within the prescribed range when the user presses the Enter key. In addition, this text-entry object is actively polled for changes by the main event loop that drives the GUI. When the value in the text-entry box is changed, the event loop queries the new value and prints this value to standard error. The code for the event loop is encapsulated in a function called process GUI behavior. The text-entry box itself, an object of class Ival Text, provides public methods with which the event loop can make these queries. Unfortunately, this design suffers from two problems. First, the monitoring code in the event loop operates on an object of class Ival Text. This complicates replacing the text-entry box with another widget -- say, a graphical slider -- that allows the user to enter an unsigned integer in some range. As it just so happens, we have a class Ival Slider that we would like to use in some configurations as a replacement for text-entry objects. It should be easy to swap out an Ival Text with an Ival Slider, but the current design does not allow this. The second problem is that while there is a reset button in this application, at the moment, it doesn't do anything. We would like to extend class Button so that it is easy to make objects (in this case Ival Slider or Ival Text objects) collaborate with the button. To complete this assignment, you will make use of the adapter and observer patterns. The adapter pattern allows you to extend existing classes so that they can be used with a new interface. This will allow you to solve the first problem described in the above paragraph. The observer pattern is used to have certain parts of your program notify other parts when an event occurs. You will use this to complete the reset button. For more information on these two patterns, pages see 139-150 and 293-303 in the Design Patterns book.
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Tasks
1. Problem #1: (a) Import the contents of /user/cse335/S09/H5-src/ into a new branch in your SVN repository named H5. To review from past homeworks, you can accomplish this by logging in to black and running the following sequence of commands: > setenv REPOS file:///user/cse335/S09/homework-repos/USERNAME > cd /user/cse335/S09/H5-src/ > svn import ./ $REPOS/branches/H5 Once you have done this, you can move back into your home directory and check out a working copy of the new H5 branch. You should see several new files. (b) Design an interface class called Ival, that abstracts the public interfaces of both Ival Text and Ival Slider. Modify the existing code to work with this interface instead of assuming that Ival Text will be used everywhere. After your modifications, it should be possible to edit app.cpp to use either an Ival Slider or an Ival Text object without having to recompile process GUI behavior.cpp. 2. Problem #2: (a) Create an interface called Button Listener that provides an operation button pressed, which will be invoked with the label of the button that is pressed. It is intended that any object that implements this interface will be able to receive button pressed events. (b) Now go modify class Button to: i. allow objects that implement the Button Listener interface to register interest in button pressed events, and ii. notify all registered li...