Java,Java, Java Ch 6 Lab: Fire Extinguisher

Ch 6 Lab: Fire Extinguisher

Authors: Ralph Morelli
Trinity College, Hartford, CT
For use with Chapter 6

Brief Description

This is a lab that is suitable for Chapter 6. It requires a conditional loop. It uses a simple applet interface, including TextArea and TextField components. This lab requires students to take more of a role in designing their solution. It asks that they prepare a design document -- including UML diagrams and pseudocode descriptions of the key algorithms involved -- before beginning to code.

Objectives

The objectives of this lab are:

To give practice designing an object-oriented program.
To give practice using simple conditional loop constructs.

Problem Statement

Suppose you determine that the fire extinguisher in your kitchen loses X percent of its foam every day. How long before it drops below a certain threshold (Y percent), at which point it is no longer serviceable? For example, if your extinguisher loses 0.1% per day (X = 0.1) and its serviceable threshold is 86% (Y=86), then it will no longer be serviceable after approximately 14 days, which equals approximately 2 weeks. (It won't be exactly 14 days because it loses 1% of it current amount of foam each day. For example, suppose it has 100 ounces of foam to start with. Then on the first day it will lose 1% of this, which is 1 ounce, leaving it with 99 ounces. On the second day, it will lose 1% of 99 ounces, which is less than 1 ounce. And so on.)

Write a Java applet that lets the user input the values X and Y and then reports how many weeks the fire extinguisher will last.

Before Lab

Study Chapter 6 of Java, Java, Java, 3E and read this document carefully.

Object Oriented Design

Before creating your Codewarrier project and before beginning to code your solution, you must hand in, for approval, a design document containing the elements described below. This should be done within the first hour of lab, and must be approved before you can start writing code

GUI Design

Follow the GUI design shown in the demo program. This involves two input TextFields and an output TextArea. The TextFields should all be associated with ActionListeners.

Object Decomposition and Class Design

What objects will your solution use? Follow the design shown on pages 314-318, which utilizes two objects, an applet that serves as a user interface and a computational object, which handles the computation of the fire extinguisher's loss. Let's call the computational object FireExtinguisher. For each object, draw its UML class diagram showing its name, instance variables, and its public and private methods.

One public method that your FireExtinguisher class should have is something like the calculateLifetime() method. This is the method that the applet will call to calculate the fire extinguisher's serviceable lifetime. HINT: What additional parameters does this method need? What type of value will it return?

Method Design

For this project your applet methods, such as init() and actionPerformed() can be modeled after the applets you designed in previous labs. The init() method should instantiate the GUI components used by the applet and add them to the applet. The actionPerformed() method should input the values that the user typed into the TextFields and pass them to the FireExtinguisher object to perform the calculation.

For the FireExtinguisher you'll need the calculateLifetime() method. (This might be all you need for this problem???)

Algorithm Design

There are two algorithms that you need to think about in detail before you begin coding. One is the algorithm for the applet's actionPerformed() method. The other is the algorithm for the FireExtinguisher object's calculateLifetime() method. Write out pseudocode descriptions of both of these algorithms.

Implementation

After your design documents have been approved, you may create your CodeWarrier project and begin coding your solution. Your code should closely follow your design.

Use the stepwise refinement approach as you develop your code, compiling and testing short segments of your code at each stage. Here are some appropriate steps:

Create the applet's layout, up through init(). Compile and Test.
Create the applet's event handling, initially just echoing the user's input in the TextArea. Compile and Test.
Create the FireExtinguisher object and test passing a value between the applet and its calculateLifetime() method. This method can just return the value it is passed for this stage. Compile and Test.
Develop and test the algorithm to test the fire extinguisher's lifetime.

Optional

Perform error checking on the user's input values. In particular, the threshold value must be a number between 1 and 100.

Hand in

Hand in your appropriately documented source code.