The purpose of this assignment is to introduce you to programming in Java and familiarize you with the mechanics of preparing and submitting assignment solutions. Your goal this week is to learn to use DrJava for editing programs, javac for compiling them, java for executing them, and Moodle for submitting them.

Hello, World.  In this step, you will setup an environment for developing Java programs.

• Working at home. If you want to work on your home computer, follow the step-by-step instructions for your operating system: Windows, OS X, or Linux. If you're on the Princeton network, then you can download the files faster via our ftp server. If you are familiar with your operating system, you should be able to finish this part on your own. If you are hesitant, bring your laptop (and a network cable) to Friend 016 or 017. The labs are staffed in the evenings with knowledgeable TAs who can assist you. Don't be afraid to ask for help.

• Working in a public cluster. If you prefer to work in one of the OIT public clusters follows the instructions for the Windows or OS X depending on your which type of computer you will be using, but skip the steps that involve installing software. If you are hesitant, work in Friend 016 or 017. The labs are staffed in the evenings with knowledgeable TAs who can assist you. Don't be afraid to ask for help.

Programming.  In this part, your job is to write four short programs. We'll assume that you've already created, compiled, and executed HelloWorld.java by following the instructions in the previous part of the assignment. Before completing this part, you should read Sections 1.1 and 1.2 in the textbook.

1. Using strings. Write a program HiTwo.java that takes two names as command-line arguments and prints them out as part of the greeting specified below.

   % java HiTwo Alice Bob
   Hi, Alice! Have you met my friend Bob?
   

   % java HiTwo Mickey Minnie
   Hi, Mickey! Have you met my friend Minnie?
   

2. Boolean and integer variables. Write a program Ordered.java that reads in three integer command line arguments, x, y, and z. Define a boolean variable isOrdered whose value is true if the three values are either in strictly ascending order (x < y < z) or in strictly descending order (x > y > z), and false otherwise. Print out the variable isOrdered using System.out.println(isOrdered).

   % java Ordered 10 17 49
   true
   
   % java Ordered 49 17 10
   true
   
   % java Ordered 10 49 17
   false
   

3. Floating point numbers and the Math library. As you might remember, there is a trigonometric identity:

   sin ²x + cos ²x = 1.

   Write a program SinCos.java that reads in a double value x from the command line, computes

   sin ²x + cos ²x

   and prints out the result. Note that Math.sin(x) returns the sine of x and Math.cos(x) returns the cosine of x, where x is an angle measured in radians.

   % java SinCos 0.534
   1.0
   

   % java SinCos 1.0
   1.0
   

4. Type conversion.   Several different formats are used to represent color. For example, the primary format for LCD displays, digital cameras, and web pages, known as the RGB format, specifies the level of red (R), green (G), and blue (B) on an integer scale from 0 to 255. The primary format for publishing books and magazines, known as the CMYK format, specifies the level of cyan (C), magenta (M), yellow (Y), and black (K) on a real scale from 0.0 to 1.0.

   Write a program RGBtoCMYK.java that converts RGB to CMYK. Take three integers red, green, and blue (not all zero) from the command line, and print the equivalent CMYK values using these formulas:

   

   Hint. Math.max(x, y) returns the maximum of x and y.

   % java RGBtoCMYK 75 0 130       // indigo
   cyan    = 0.423076923076923
   magenta = 1.0
   yellow  = 0.0
   black   = 0.4901960784313726
   

Writeup.  With each assignment you must submit a text file named readme.txt that is a narrative description of your work. We provide a readme.txt that you should use as a template. Download this file and answer all questions in the space provided.

Browsing the course website.  The next part of the assignment is to browse the COS 126 Web pages. The address is:

http://www.princeton.edu/~cos126

Submitting the assignment.  The final part of the assignment is to submit HiTwo.java, Ordered.java, SinCos.java, RGBtoCMYK.java, and readme.txt via the Web submission system. To do this, go to the course webpage and select the HelloWorld assignment under Social Activities. Be sure to hit the Run Script button to check your program against our Java compiler. It should compile without errors or warnings; if not, fix the problem and resubmit it. To submit a file, you must be officially registered for the course.