Ch 2 Lab: The Temperature Class

Authors: Ralph Morelli & Bronzell Dinkins
Trinity College, Hartford, CT
For use with Chapter 2

For Instructors

This is an ambitious lab for Chapter 2. It asks students to use the Riddle class, discussed in Chapters 1, as a model in building the Temperature class. They are asked to draw a UML diagram of the Temperature class and to translated that into a written specification. At this point (Chapter 2), we haven't really explained how methods and parameters work, so they have to be willing to take these parts on faith.

An optional section of the lab walks through using command-line input with the BufferedReader object. No attempt is made to explain how I/O works, so this too must be taken on faith. As in preceding labs, this lab emphasizes the stepwise refinement coding techniques.

Objectives

The objectives of this lab are:

To give practice designing a simple Java class to convert temperatures from degrees Fahrenheit to degrees Celsius.
To convert the design into a working Java program
To compile, run and test the Java program

Before Lab

Read Chapter 2 of Java, Java, Java, 3E. Read through this document and bring your textbook to lab.

Problem Statement

Design and implement a class for a Temperature object that is capable of reporting its temperature in either Fahrenheit or Celsius. This class should have one instance variable called degrees, which contains the Fahrenheit temperature, and two public methods, one called getFahrenheit(), which returns the temperature in Fahrenheit, and one called getCelsius(), which returns the temperature in Celsius. This method has to convert the stored temperature to Celsius before returning it. An expression for converting Fahrenheit to Celsius is (5 *(F -32) /9), where F is the temperature in Fahrenheit.

Test your class definition by implementing a main() method that creates Temperature instances and displays their temperature values.

Your program should produce something like the following output in the Java console:

 The Fahrenheit temperature of thermometer1 is 20.0 degrees.
 The Celsius temperature of thermometer1 is -6.67 degrees.

 The Fahrenheit temperature of thermometer2 is 98.6 degrees.
 The Celsius temperatureof thermometer2 is 37.0 degrees.

Problem Decomposition

This problem can be divided into one class, the Temperature class, which will implement the temperature conversion. It will contain a main() method in which Temperature instances will be created and used.

Design

Step 1. Draw a UML class diagram to describe the design of the Temperature class. Your design should identify the of the class, its attributes (instance variables) and behaviors (methods). Designate which elements will be hidden and which parts of the class will make up its public interface. Model your design after the the Riddle class discussed in Chapter 1 of Java, Java, Java, 3E.
Step 2. Develop a written specification for the Temperature class based on your UML diagram. This will become a comment block at the beginning of your source file.
Step 3. Create a CodeWarrior project named Lab2, using the Java Application Stationary, and saving the project on your desktop. Don't forget to rename the TrivialApplication class to Temperature and make the corresponding change to the name of the Java source file and to the project's target. If you can't remember how to do this, consult Lab 0: Metrowerks CodeWarrior.
Step 4. Type the specification you developed in Step 2 into a Java comment block and save it in a file named Temperature.java. This file will be the file you use for defining the Temperature class. The comment will serve as documentation for the program. A comment block in Java begins with either "/*" or "/** " and ends with "*/". It can extend over multiple lines. As explained in Appendix A, comments that begin with "/**" are documentation comments, which can be automatically turned into documentation for the class by using software that comes with the Java Development Kit (JDK). You sould use documentation comments to describe a class's specification. Here's an example format that you can use:

/** * Class Name: Circle * * ... ( the rest of your specification ) * */

Implementation

Have your UML diagram and Design Specification checked by the Lab Instructor or TA before beginning the implementation phase.

Step 5. Use the stepwise refinement approach that we practiced last time to code and test the Temperature class. Here's a sequence of appropriate steps, after each of which you should compile and run your program.
1. Code the initial comment block (purpose of your program, your name, lab section, etc) and the basic class definition.
2. Code the declarations for the class's instance variables as well as the constructor method.
3. Code the definition for each method, one at a time.
4. Code a stub version of the main() method.
5. Add code to the main method to create and use one Temperature object. Write one access method at a time, as well as a method call in main() that tests the method. Here is where you would use method calls embedded within println() expressions to display the temperature values. For example, here are several statements that will output thermometer1's temperature:
  
  System. out. print(" The Fahrenheit temperature of thermometer1 is "); System. out. print( thermometer1. getFahrenheit()); System. out. println( " degrees.");
6. Add code to the main method to create and use a second Temperature object.

Optional

NOTE: This section is required if you complete all other lab activites before 3:30 PM.

If time and energy permits, you may want to try this optional exercise, which makes use of Java's input class, BufferedReader.

Before a user can enter tempurature values from the console, you must set the CodeWarrior Java MacOS Setting targetRedirect stdin.

Make sure that "Redirect stdin" is set to the "Message Window" so that Code Warrrior will take input from the keyboard as you type it.

Incorporate the following code into your main() method that allows the user to input a value for a temperature.

The following statements must be incorporated into your program (IN THE CORRECT LOCATIONS):

  import java.io.*;             // The IO classes must be imported
  ...
  public static void main(String argv[]) throws IOException // Main must be revised
  ...
    // The following code should be added to the main() method

  BufferedReader input = new BufferedReader( new InputStreamReader (System.in) );
  String inputString;
  double temp;

    // The following code is used to input a double value and store it
    //  in the temp variable

  System.out.println("Input a temperature in Fahrenheit degrees: " );
  inputString = input.readLine();
  temp = Double.valueOf(inputString.trim()).doubleValue();

   // The following statement could be used  to create a Temperature 
//object using the input value.

Temperature thermometer1  = new Temperature(temp);

Lab Checkout

Have your work checked by the lab instructor before you leave the lab. Make sure to include your name and the lab section in files.