COS 126

Assignment 0: Hello, World
Programming Assignment


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. You will learn to use DrJava editor for writing, compiling, and executing Java programs, and Dropbox for submitting your work electronically.

Setting up a Java programming environment.  In this step, you will set up a Java programming environment, either on your computer or on an OIT public cluster machine.

If you are familiar with your operating system, you should be able to finish this part on your own. If you encounter difficulties, please consult the undergraduate lab TA schedule and go to Lewis Library 121 for assistance. Don't be afraid to ask for help.

Programming.  In the previous step, you created, compiled, and executed Next, you will write two four short programs on your own.

  1. Hello, World. Type in everyone's first program—
    % java HelloWorld
    Hello, World
    You will need to make one minor edit: change the header to match the format prescribed in the Assignment FAQ.

  2. Strings and command-line arguments. Write a program that takes four first names as command-line arguments and prints a proper sentence with the names in the reverse of the order given. Here are two sample executions:
    % java HiFour Alice Bob Carol Dave
    Hi Dave, Carol, Bob, and Alice.
    % java HiFour Alejandro Bahati Chandra Deshi
    Hi Deshi, Chandra, Bahati, and Alejandro.

  3. Integers. Read Section 1.2 (through page 23) of the textbook. Write a program that takes three int command-line arguments and prints the three integers and their sum in the form of an equation.
    % java SumThree 2 5 8
    2 + 5 + 8 = 15
    % java SumThree -2 5 -8
    -2 + 5 + -8 = -5

  4. Integers and booleans. Write a program that takes three int command-line arguments, x, y, and z. Define a boolean variable 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.
    % java Ordered 10 17 49
    % java Ordered 49 17 10
    % java Ordered 10 49 17

    Restriction: You may not use if statements on this assignment.

  5. Floating-point numbers and the Math library. The great circle distance is the shortest distance between two points on the surface of a sphere if you are constrained to travel along the surface. Write a program that takes four double command-line arguments x1, y1, x2, and y2 (the latitude and longitude, in degrees, of two points on the surface of the earth) and prints the great-circle distance (in nautical miles) between them. Use the following formula, which is derived from the spherical law of cosines:
    \( \textrm{distance} = 60 \arccos(\sin x_1 \sin x_2 + \cos x_1 \cos x_2 \cos(y_1 - y_2)) \)
    This formula uses degrees, whereas Java's trigonometric functions use radians. Use Math.toRadians() and Math.toDegrees() to convert between the two. For reference, a nautical mile is 1/60 of a degree of an arc along a meridian of the Earth (which is approximately 1.151 miles).
    % java GreatCircle 40.35 74.65 48.87 -2.33      // Princeton to Paris
    3185.1779271158425 nautical miles
    % java GreatCircle 48.87 -2.33 40.35 74.65      // Paris to Princeton
    3185.1779271158425 nautical miles

  6. 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 that converts from RGB format to CMYK format. Your program must take three integer command-line arguments red, green, and blue; print the RGB values; then print the equivalent CMYK values using these mathematical formulas:

    \( \begin{align*} white \;&=\; \max \left \{ \, \frac{red}{255}, \, \frac{green}{255}, \, \frac{blue}{255} \, \right \} \\ cyan \;&=\; \Bigl(white - \frac{red}{255} \Bigr) \; \div \; white \\ magenta \;&=\; \Bigl(white-\frac{green}{255}\Bigr) \; \div \; white \\ yellow \;&=\; \Bigl(white-\frac{blue}{255}\Bigr) \; \div \; white \\ black \;&=\; 1 - white \end{align*} \)
    % java RGBtoCMYK 75 0 130    // indigo
    red     = 75
    green   = 0
    blue    = 130
    cyan    = 0.423076923076923
    magenta = 1.0
    yellow  = 0.0
    black   = 0.4901960784313726
    % java RGBtoCMYK 255 143 0   // Princeton orange
    red     = 255
    green   = 143
    blue    = 0
    cyan    = 0.0
    magenta = 0.4392156862745098
    yellow  = 1.0
    black   = 0.0

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

    Restriction: You may not use if statements on this assignment, but you may assume that the command-line arguments are not all simultaneously zero.

For full credit, your programs must not only work correctly for all valid inputs, but they should be easy to read. You are expected to follow these style guidelines in this course. In particular, you must include a header (name, NetID, precept number, and a brief description of what the program does) in every file you submit, using the prescribed header format.

More things to do. 

  1. Writeup.  Submit a text file named readme.txt that is a narrative description of your work. Each week, we provide a readme.txt file for you to downoad and use as a template, answering all questions in the space provided.

  2. Questionnaire.  Complete the following brief questionnaire.

  3. Collaboration policy quiz.  Read the course collaboration policy and take a short quiz on the policy (available in Blackboard). You must repeat the quiz until you answer all questions correctly; otherwise, you will not receive credit on any programming assignment.

  4. Treasure hunt.  Browse the COS 126 website and complete the Treasure Hunt (available in Blackboard). It is essential that you understand what's where and how to get to it.

  5. Submitting the assignment.  Submit,,,,,, and readme.txt via the Web submission system called Dropbox. To do this, click the Assignments link from the course website; click the Submit link for that assignment; login using your OIT NetID (if necessary); and upload the specified files. Finally, click the Check All Submitted Files button:
    Check All Submitted Files button
    This will compile and execute your programs, alerting you to potential problems before we grade your work. Fix any problems and resubmit.

Getting help. If anything is unclear, don't hesitate to drop by office hours or post a question on Piazza. We also recommend reading the checklist, which provides some clarifications and answers to frequently asked questions.

Challenge for the bored (not extra credit). Redo without using the comparison operators (<, <=, >, and >=). Redo without using Math.max(). Do not use if statements for either one. Even if you solve these, please submit your original solutions, which are likely to be simpler and easier to read.