Lab 3: Introduction to BlueJ

For the TA
- This lab is self-explanatory, just let the students work out the lab for themselves.
- You only need to assist students when they have questions.
Lab goals
- In this lab you will learn how to edit Java files with BlueJ by writing a short Java program FtoC.java.
- The deadline for completing this lab assignment is midnight, today.
  Please, make sure that you have added the honor code statement at the top of the lab project file Euclid3.java (that you will obtain per instructions below):
  Also, make sure that the Euclid3.java is inside your cs170/lab3 directory ( i.e., inside /home/_your_id_here_/cs170/lab3/)
Reading material
You should read the material before coming to the lab. If you have not done so, try to following the instructions in this webpage (they are very detailed and self-explanatory).
You should read the webpages above after the lab to re-enforce what you have learned.
What you will be doing in this lab:
If you cannot finish this during the lab time, then it is due by midnight today.
Preparation: Create your ~/cs170/lab3/, and copy the prepared files
- Copy-and-paste these commands into a terminal window:
Launch BlueJ

Open ~/cs170/lab3 as a BlueJ Project

Use these steps open the directory ~/cs170/lab3 as a BlueJ Project:

Click "Project" and "Open Non BlueJ...":

A file chooser window appears, probably listing the contents of your home directory:

Do these steps inside the file chooser window:

Navigate to your cs170 directory (double-click on the cs170 folder), and then
select, but do not enter, lab3 (click once on the lab3 folder):
(The File name: field should now show "lab3").
There should also be some text to the right saying "Preview of possible package structure" with "Euclid3" below)

Hit "Open in BlueJ".
You should see a new window titled "BlueJ: lab3".
Inside the window there are a few buttons, and two icons that correspond to files.
One icon looks like a sheet of blank paper (it represents a potential text file called README.TXT) and the other icon represents your FtoC.java file.

Using the terminal application, you can verify that this worked by listing the contents of ~/cs170/lab3 (which you just created). Type this command in a terminal window:

    ls ~/cs170/lab3

you should see FtoC.java along with a file called package.bluej.

Important notes on BlueJ:

The presence of the file package.bluej indicates that the directory is now a "BlueJ project".
Don't edit this file, because BlueJ uses it to store project details.
If you remove the file package.bluej, then the directory becomes an ordinary directory (and is no longer a BleuJ project)

Common problems experienced by students with BlueJ:

Important fact:
That means if you made a directory into a BlueJ project by mistake, you cannot browse the sub-directories !!!
If you make a directory into a BlueJ project by mistake, you can undo this by remove the file package.bluej from that directory:

Compile and run Java programs using BlueJ (click here if you read the lab reading material)

Note:

The following instructions is used to compile a Java program named Euclid3.java
To compile and run the FtoC.java program, you perform these steps on the FtoC.java file.

How to compile (= translate) and run (= execute) the Euclid3.java program:

To compile the Euclid3.java program with BlueJ:

RIGHT-click the Euclid3 icon in the BlueJ: lab3 project window and select Compile:
If successful, the Euclid3 icon will become unshaded:

If there are compile errors, you need to fix them with the BlueJ editor and re-compile the program until all errors are corrected.

You can only run (= execute) the Euclid3 program after it has been compiled successfully.

To run the Euclid3 program with BlueJ:

RIGHT-click the Euclid3 icon in the BlueJ: lab3 project window and select the main() method:
A method call window will appear:
where you can enter the parameters for the main() method.
The main() method in Euclid3 does not use any parameters, so just click OK.
When Euclid3 is run, a output window will pop up with the results:

Important note:

When you write a Java program, you will go through the compile and run process many times to test whether your program is correct
So remember the compile and run steps (see above) to perform the TODO's in the next section.

A brief intro to method

In this lab, you will work with a new concept that has not been discussed in class. It's called a method.

Let me give you an example:

public class Demo { /* ------------------------------------- Define the method f(x) = x^2 ------------------------------------- */ public static double f( double x ) { double y; y = x * x; // square of x return ( y ); // Return the value y (which is equal to x^2) } public static void main(String[] args) { double x = 3.0; double y; y = f(2.0); System.out.println(y); // will print 4.0 y = f(x); System.out.println(y); // will print 9.0 } }

A method can receive input parameters (in this example: 2.0 and x) and use the input parameter to produce an output value.
A method returns the computed output value using a return statement:

Lab Assignment

Write the statements given in the FtoC and CtoF methods inside the FtoC.java file.

Example:

public static double FtoC(double x) { // input: x = temp in degree in F // Compute: r = temp in degree C double r; // Write these statements: // 1. compute: x - 32 and store result in variable r // 2. then multiply r by 5 and store in r // 3. then divide r by 9 and store in r // 4. then return r }

Note:

You must write the individual assignment statement specified.
(We want you to get used to the BlueJ editor)

Short note on using the BlueJ editor:

Scroll to the location where you want to change the text
Click on the location where you want to make a change
Type text to add text, and hit the DELETE key to remove text.

(Note the editor will help you do indentation semi-automatically, if you let it.)

Run your code!

To test your code, "Close" the editor and right-click the "FtoC" icon.
Select "Compile".
Once it is compiled, you can select "void main(String[] args)".
A popup box appears asking you for the value of args, but the default is fine, so hit "OK".
When the program is run, a "BlueJ: Terminal Window" should appear, where you can see the output of your program.

If problems remain, go back and edit again.

When you are done, Quit BlueJ (and turn in your work)
Note:

Turn in
- When you are done (or not done for partial credits), you must turnin your work with these commands (issued from a Terminal window):
  This makes a copy of your work (FtoC.java this time). It does not check your work for correctness. Your turnin is successful when you see this message:
```
    Program `FtoC.java' has been turned in by YOUR_ID as lab3
```
  You may "turnin" multiple times ---- a later turnin will overwrite you previous turnin version. So only your last version will be graded.
  
  For the Lead TA:
Additional exercise: if you are serious about becoming a Computer Science major, do the additional exercise to hone your editing and programming skills.

Additional lab exercise

Open the program Extra.java in Bluej.
Write at the place indicated program statement to exchange the values in the variables x and y
Note:

Hint:

Imagine you have a glass of water and a glass of wine.
And you need to exchange the content in the glasses.
How do you do that ?

In terms of a computer program:

A glass is a variable
What is contained inside the glass is the value of the variable.
We want to exchange the content of the variables...
Do the same steps as you would do to exchange the content of 2 glasses.

You don't need to turn in the additional lab exercise, but you can get help from the TA to work on the problem.