CS 2102 - B18

Lab 1 - Setting up your environment; Java classes

Lab Objectives

• Get your Java environment configured, including JUnit for testing
• Create a simple class, with Examples class and a test case
• Know how to run your tests
• Check that you can submit homework structured for automatic grading
• (if time) Create a nested class reference

Preliminaries

• Sign the attendance sheet.

• If you already know Java or have your environment configured, jump to the optional problems on creating nested Java objects.

• Please make sure you submit your work to InstructAssist by the end of the lab. We are not grading your lab work, but we are going to use this submission to check that you know how to submit files such that the autograding scripts can process them. This will hopefully catch many configuration errors before it counts on the first homework.

What you should do

Setting up your Java environment

• Eclipse Set-Up Instructions

If you are using the lab computers, type "Eclipse" in the search box under the programs menu on the lab machines.

If you are using your own laptop, download and install Java and Eclipse as discussed in the instructions above. If you are on a Mac, note that you need to download/use the "JAR File", not the "Mac OS X App".

Creating a basic Java program

1. Create a new project and open a new file in your chosen environment. Copy the following class definition into the new file:

         class Song {
          String title;
          int lenInSeconds;  // duration of the song  
   
          Song (String title, Integer lenInSeconds) {
           this.title = title;
           this.lenInSeconds = lenInSeconds;
          }
         }
   

2. Add this Main.java file to your project. Java looks for a function (a.k.a. a "method" in Java) named main to call to start running your program. We have given you this main method, enclosed in a class (for reasons we will explain later this week).
3. To check for typos and notation errors in your program, press the icon in your enviroment to compile your program. In DrRacket, you used to hit a single Run button. In Java, you do two steps: compile (which checks for a bunch of notational and other errors) then run (which actually runs your program).

Adding examples and tests

1. First, create some objects (a.k.a examples of data in 1101 terms). Define two song objects in the Examples class, each through code such as

         Song HapBD = new Song("Happy Birthday", 18);
   

   Compile and run your program. You should get the same message as before, reporting that your program ran.

2. Now we will create a test case. Test cases are a kind of function; Java uses the term methods instead of functions. Since you haven’t learned how to write methods yet, in today’s lab we will simply copy the code to create a test that checks the lenInSeconds value in one of your Song objects. This is not an interesting test, but the goal is to make sure you can set up a test while you have the staff around to help.

   Copy the following code into your Examples class.

         @Test
   
         public void checkHBLen() {
            assertEquals(18, HapBD.lenInSeconds);
          }
   

   What is this code saying? In JUnit the @Test labels a test case. The next line defines a method called checkHBLen that takes no arguments. The method uses the built-in assertEquals to ask JUnit to make sure that the two expressions produce the same answer (similar to check-expect from cs1101). The first argument to assertEquals should be the expected answer and the second should be the computed answer.

   Ignore the public void part for now – we will explain those in the next couple of classes. For now, just include them when you write a test case.

   Compile and run your project. You should get the same message you have been getting.

3. Add another test that has the wrong expected answer (and hence should fail). Run your tests again to see how your programming environment reports failed test cases.

   Note to those who already know JUnit: you may put your tests in other (multiple) classes, as long as those classes have Examples or Test as part of the class name.

Submit your work (instructions at bottom), to make sure you know how to submit assignments.

Everyone should finish up to this point.

If you have time: nested class references

1. Define a class for albums, which contain two strings. One is the name of the artist; the other is the genre of music ("Rock", "Jazz", etc) that is on the album. You can put this class in its own file (proper Java style) or in the file with your Song class (easier to follow as you are learning Java)
2. Edit your Song class to include a field onAlbum with type Album.
3. Revise your examples of Song data to include the new Album field.
4. Add a test case that checks the genre of a Song object.

What to Turn In

If you don’t have an account in InstructAssist, ask your lab staff for help.