Objectives:

• Develop an immutable class
• Create methods that accept an object of the class as a parameter
• Create methods that return an object of the class

Background:

Materials:

• Main.java
• Color139.java

Part 1:  Getting Started

1. Setup your program environment by creating a new folder named lab14a.


2. Download a copy of the Main.java file. This file implements the main function you will use to test your implementation of Color139.


3. Download a copy of the Color139.java file. Read the documentation for the Color139 class that this file implements.

Part 2:  Implementation

1. Look at the parts of Color139 that have already been completed.

   • A number of constants have been defined. Those constants are public so they may be used outside of the class (you should note those constants are referenced in Main.java).

   • Three instance variables are defined. Thus every object that is created will have its own copy of those three instance variables. Those instance variables are private so they can only be accessed by methods in the class.

   • The methods toString, dim, and add have already been defined. Look at those methods and ask questions about anything that you do not understand.

2. Implement the constructor method. Recall that a constructor's job is to initialize an object to a particular state. In this lab, your color class's state will not change after it is initially created. Compile your java files and run the main program as specified below. The top portion of the html file that outputs the constants should work properly. Debug your Color139.java file as needed. Click here for a sample of what your program should produce.

3. Implement the other methods, one at a time. Rerun the program after implementing each method to test the implemented method. Make sure a method is working correctly before moving on to the next method.

4. When you have everything working, open two browser windows: one with your web page and one with the sample output page. Ask your instructor to check off that you have gotten your program to produce the correct output. There are no submissions for this lab.

Running Your Program

1. In addition to running your java programs within an IDE, you can run your java programs from the command line. To use java from the command line, you must first change your working directory to be the working directory that holds your java files.

   If you have already compiled your java files in jGrasp or DrJava, you do NOT need to compile them again. But if you want to compile your java files from the command line, enter the following command.
         javac *.java
   If you have many errors and want to limit the number of error messages displayed, enter the following alternative command.
         javac *.java 2>&1 | head -20

   Normally, to run a java program that has the main in a file named Main.java, you would run the following command.
         java Main
   But instead of sending the program output to the screen, we want the output to go into a file. So for this program, execute it with the following command.
         java Main > output.html
   This will create a file named output.html which you should view in a web browser.