Lab 1 -- Using Java in the BlueJ IDE

Computer Science 202
Introduction to Programming

Fall 2012, The College of Saint Rose

Lab 1: Using Java in the BlueJ IDE
Due: 11:59 PM, Monday, September 10, 2012

This first lab assignment introduces you to the tools that you will use this semester. Your task is to type in and run a Java program that prints a simple message.

Setting Up Java and BlueJ

This assignment assumes that you either using a school computer that already has BlueJ installed or that you have already set up Java and BlueJ on your own computer.

Writing and Running a Java Program in BlueJ

We will use the program we looked at in class as a starting point.

/* A Hello World example in Java */

public class HelloWorld {

   public static void main(String[] args) {

     String message = "Hello, World!";
     System.out.println(message);
   }
}

So let's go through the steps to set up, type in, and run this program in the BlueJ environment.

We type our program in a text editor. The program we type in is called the source code. Usually, each Java class we write will be placed in its own source code file, with a .java extension.

We will use a text editor that is part of an integrated development environment called BlueJ. BlueJ is a free program, indended for use by beginning Java programmers. It is available for Windows, Mac, and others, so you will be able to develop your Java programs on any computer where you want to install BlueJ.

Create a folder, either in your network storage on a school computer, or in an appropriate place on your own computer, where you will keep your work for the course. A good name might be CSC202.
Within that folder, create a folder for this lab. Lab1 might be a good name.
Launch BlueJ.
Once in BlueJ, we create a new project. In the window that pops up, navigate to the Lab1 folder your just created, then use the File: box at the top of the window to name it HelloWorld. This should bring up a project window with the title "BlueJ: HelloWorld".
Choose "New Class...", and create a class named HelloWorld. This should add a box labeled HelloWorld to your project window. It will also create a new folder for this project.
Double-click on the box labeled HelloWorld to open the HelloWorld.java source code file.
BlueJ provides the skeleton of a class, most of which is not helpful to us at this point. Delete everything in the body of the class.
Type in the main method from above inside the body of the class.
Press the "Compile" button. If everything is correct, you should see a message at the bottom "Class compiled - no syntax errors". If there is an error, BlueJ will attempt to tell you where the error is.
Now we are ready to run the program. To do this, right-click on the HelloWorld box in the project window, and choose "void main(String[] args)" from the menu. Click "OK" on the window that pops up.
This should bring up another window, the terminal window, through which you will interact with the program. Since this program only prints a message, you should see that message in the terminal window.

That's it - you have successfully written, compiled, and run a Java program.

Adding Comments

Documentation is an important part of writing a program. Comments are the mechanism we will use to provide that documentation. Documentation is essential to help the author of a program as well as others who may need to read or perhaps modify the program at a later time.

We have seen that Java allows us to write comments on a single line that begins with // or that span multiple lines when enclosed in a /* and */ pair.

Every program you write should include comments. Part of your grade for every program you submit this semester will depend on how well you comment your code.

You should always include at least these kinds of comments:

A class comment at the top of each Java file. This must include your name (or names, for group work), the course number, which section you are in (just give the starting time), the assignment name and/or number, and the date. It should also include a sentence or two that describes the purpose of the program.
A method comment for each method in your program. It should describe the parameters, return values, and a brief description of what the method does.
A comment describing each variable or group of related variables you declare.
A comment describing the purpose of any line of code whose meaning is not entirely obvious from context.

We will work together through the start of the semester to make sure everyone has a good idea of what is considered an appropriate level of commenting for our course.

For this simple program, you should include a class comment, a method comment for the main method, and a comment giving a brief description of the one variable we used. There should be no need to describe any other lines of code in this very short program.

Class examples will provide an appropriate a level of documentation.

Adding a Bit More Code

We haven't seen enough Java yet to do much more, but we can print more messages. Leave the existing message as is, but add in at least two more System.out.println statements that print more sentences.

Making it Look Nice

Java is very picky about the syntax of our Java programs, but is very forgiving when it comes to how we organize a syntactically correct Java program in terms of new lines and spaces. We could write an entire class definition on a single line and Java would not complain. However, it is very difficult for you to write and understand a program that looks messy. Therefore, you will be required to submit programs that follow strict formatting guidelines.

Fortunately, BlueJ helps us out here. It tends to indent things nicely, and as long as you don't try to put multiple statements on a single line, your programs should exhibit reasonably good formatting. To ensure this, before you submit any program (and periodically while you are developing it, if the formatting starts to look ugly), you should run the "Auto-layout" command from the "Edit" menu in BlueJ.

Lab Questions

Please answer the following questions, placing your responses in an additional comment at the end of your Java program. You may refer to the text or class notes to help answer as needed.

Question 1: What color does BlueJ's editor use to indicate single-line comments? Multi-line comments? (1 point)

Question 2: What colors does BlueJ's editor use to indicate each Java keyword in your program? (1 point)

Question 3: What color does BlueJ's editor use to indicate a string constant (like "Hello, World!")? (1 point)

Question 4: BlueJ also uses lightly shaded boxes or white boxes to help you to determine which code is part of which class or method headers and/or bodies. You should see 4 such boxes in your program. Describe what part of your program (i.e., which class definition, class body, method definition, or method body) is enclosed in each of these boxes. (2 points)

Question 5: What file does the compiler produce if it successfully compiles a .java file? See if you can find this file in the folder that contains your BlueJ project. (1 point)

Submitting Your Work

Before 11:59 PM, Monday, September 10, 2012, submit your Java program for grading. Please upload your Java source file (the one with the .java file extension, and only that file), including the comment at the end that includes your responses to the lab questions, to Blackboard using the submission procedure in the "Labs" section. Note: if your computer does not show any files in your project folder with a .java file extension, you should change your folder's properties so it does show file extensions. You should be able to do this in either Windows or Mac environments, but don't hesitate to ask if you have trouble doing so.

Grading

This assignment is worth 15 points, which are distributed as follows:

> Feature	Value	Score
`HelloWorld.java` original message	3
`HelloWorld.java` extra messages	2
`HelloWorld.java` comments	3
`HelloWorld.java` formatting	1
Lab questions	6
Total	15