Implementation

Use the stepwise refinement approach, described in Chapter 1, to convert your specification into a Java class definition. That is, write the program in small stages, compiling and running the program after each stage is coded. This will enable you to localize any errors that are made. Remember that Java is case sensitive and very fussy about the spelling of identifiers and keywords.

Note: Rather than typing everything from scratch, another way to write this code is to copy and paste an existing program. You can download the Rectangle.java source code from the course web site. Just follow the links on

    http://www.cis.umassd.edu/~x2zhang/courses/CIS180/F03/labs/lab3/Rectangle.java

You can then modify it using cut, copy, and paste editing.

Reasonable coding stages for this project would be

• Code the header of the Circle class but leave its body empty. Code the header and an empty body for the main method, which should be coded exactly as shown in the examples in this chapter.
• Code the declarations for the instance variables as well as the constructor method. The constructor method should be closely modeled after Rectangle's constructor.
• Create a Circle instance in the main() method, so that you can use it to test the constructor. This is where you would use the operator new plus the constructor method.
• 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 circle's area and perimeter. For example, here's a pair a statements that will output circle1's area:

      System.out.print("The area of circle1 is ");
      System.out.println(circle1.calculateArea());
  

• Complete the documentation for your program. Add comments to your code that will make your program more readable. A good rule might be that you should be able to read your program two years from now and still understand what it does. See Appendix A for guidelines about documentation conventions.