1 5/8: A Little Eclipse, A Little Java

The goal of this lab is to introduce some aspects of our work environment: the Eclipse IDE and the basics of running a program in Java-like languages. In the second part of the lab, (the one that really teaches you something) will focus on data definitions and examples in a simple subset of Java language.

CCIS Login

Exercise 1. Log in to a lab computer using your CCIS credentials.

If you requested a CCIS username and password yesterday, it should be active today. Please send email to dvanhorn if you’re still having issues – we need to resolve all of these ASAP since your homework requires a working CCIS account.

Exercise 2. Verify your CCIS username in the following list:

acalo          deema           jcaron          kosof           sripley7

ajacks         dsimond         jinwow          merylas         yusuf.m

ascherj        goodwin         joejeno         michng

bjliuy         gudosha         jwall           nnamdi93

bmccabe4       guom            kevin08         psanshi

cungtran       jbrooks2        kmiao           schwarta

These are the usernames submitted in assignment 1. Make sure your username appears exactly as it does on the CCIS system. If there’s any corrections that need to be made, please inform the TA.


Exercise 3. Select a homework partner and register your selection with the TA.

You should select a partner that you feel comfortable working with for at least the first few weeks of this course. (You will have the opportunity to request a new partner in a couple weeks.) You and your partner will be responsible for developing solutions to assignments. Both of you must be able to explain, defend, and update your designs to a jury of your peers. Be sure to read about the history and motivation for Pair programming on the course web page.

Exercise 4. Exchange contact information with your partner and discuss arrangements for working together.

You should complete the rest of this lab (and future labs) working as a pair. Your lab partner doesn’t necessarily have to be your homework partner, but it’s probably a good idea for the first couple of labs so you can get comfortable working as a pair.

Eclipse IDE

In this course, we will use the Eclipse development environment to write Java programs. Eclipse is freely available and we recommend you install it on your personal computer. It is also available on all CCIS lab machines.

If you feel more comfortable, you may choose to use another IDE (e.g. NetBeans) or work directly from the command line, but you and your partner must both be comfortable with the chosen programming environment, and the staff may not be able to assist you with issues encountered in other environments.

Eclipse includes an editor and allows you to organize your work into many files that together make up a project. It has an "incremental" compiler that so you can edit and run your programs while getting relatively fast error feedback. Your Eclipse workspace can contain many projects, so you should be able to keep all your work in one workspace, with one project for each assignment or lab.

Exercise 5. Start Eclipse and create a workspace for the work in this class. Create a new project for today’s lab.

Be sure to save all of your work to a location that you can retrieve it from later. Labs will often build upon each other and you may be asked to submit parts or all of a lab as part of an assignment. In the future, you may use svn to save and keep track of the changes to your work. We will look more closely at svn in the next lab.

A Few Data Definitions

Now that you have Eclipse up and running and a project started for today’s lab, you can try your hand at developing a few data definitions in the Java notation.

Exercise 6. Develop a class-based representation of complex numbers.

Complex numbers are are used in several fields, including: engineering, electromagnetism, quantum physics, applied mathematics, and chaos theory. A complex number is a number consisting of a real and imaginary part. It can be written in the mathematical notation a+bi, where a and b are real numbers, and i is the standard imaginary unit with the property i2 = −1.

Exercise 7. Develop a class-based representation of shapes, including points, rectangles, and circles. A shape should include a pinhole, which represents the center point of the shape.

Once you have defined class definitions for complex numbers and shapes, it would be nice to create some examples. To do, define an Examples class that you can use to hold some example data. Here’s a sketch that creates some examples of fictional objects:

class Examples {



  Blah b1 = new Blah(3, 4, 5);

  Blah b2 = new Blah(8, 9, 10);


  Foo f1 = new Baz(b1, 87);

  Foo f2 = new Bix();


Exercise 8. Create an Examples class and write several examples of complex numbers and shapes.

Be sure to take note of Eclipse’s reaction when you make mistakes as you type. Try making a few intentional mistakes (like passing a complex number constructor a string) to get a feel for what goes wrong.

Now let’s work on some recursive union data definitions.

Exercise 9. Develop a class-based representation of lists of integers. Add examples of several lists of integers to your Examples class.

Exercise 10. Develop a class-based representation of lists of complex numbers. Add examples of several lists of complex numbers to your Examples class.

It’s tempting to want to abstract the above two data definitions. Identify what’s different between the two. We will discuss how to abstract such definitions in future lectures.

A Few Methods

You’ve now defined some new classes of data and made of few instances thereof. But what good is information without computation? Let’s develop a few methods, starting with some for complex numbers.

Complex numbers are so useful, it turns out they are included in the set of numeric values that Racket supports, but unfortunately Java lags behind and doesn’t support them. The Racket notation for writing down complex numbers is 5+3i, where this number has a real part of 5 and an imaginery part of 3; 4-2i has a real part of 4 and imaginary part of -2. (Notice that complex numbers generalize the real numbers since any real number can be expressed as a complex number with an imaginery part of 0.) Arithmetic operations on complex numbers work as they should, so for example, you can add, subtract, multiply, and divide complex numbers. (One thing you can’t do is order the complex numbers, so < and friends work only on real numbers.)

So if you’d like to experiment with a complex number calculator, just fire up DrRacket and use the interactions panel.

Here are a few examples written in ISL:
; Verify the imaginary unit property.
> (sqr (sqrt -1))


> (sqr 0+1i)


; Arithmetic on complex numbers.
> (+ 2+3i 4+5i)


> (- 2+3i 4+5i)


> (* 2+3i 4+5i)


> (/ 2+3i 4+5i)


; Complex numbers can't be ordered.
> (< 1+2i 2+3i)

<: expects type <real number> as 1st argument, given: 1+2i;

other arguments were: 2+3i

; Real numbers are complex numbers with an imaginary part of 0,
; so you can perform arithmetic with them as well.
> (+ 2+3i 2)


> (- 2+3i 2)


> (* 2+3i 2)


> (/ 2+3i 2)


> (magnitude 3+4i)


Exercise 11. Develop class-based analogs of the above functions on complex numbers.

We haven’t discussed testing Java programs, but we will in the next lecture. For the time being, just write examples and the expect result in the comments of your code.

Exercise 12. (Challenge) Develop a sum method for lists of complex numbers.

Note that this requires writing a recursive method (since we wrote a recursive data definition!), which we did not cover in lecture. Try to figure out how to solve the problem by analogy with how you would solve the problem in ISL.

Wrap up

You’ve now developed a few data definitions and methods in Java. Congratulations. Be sure to practice more on your own so that you can fluently solve these kinds of problems. Come prepared with questions to the next lecture.

If you would like to have your lab solutions (anonymously) critiqued by the class, send your code to dvanhorn. (This is completely optional, but highly encourage; critique is how you become a better designer.)