CS 210: Data Structures

Exercise 1: Creating a Program Using Eclipse

An object-oriented program is, as we learned in class, made up of a collection of classes.  Each class is stored in a separate file, where the name of the file is the name of the class with a .java extension.  Thus, a class called Aquarium must be in the file Aquarium.java.  We might have many classes in a program, and we might have many programs.  How do we keep track of which classes are part of which programs?

The Eclipse development environment uses the idea of a project to keep track of information about a program, such as which classes are part of the program, where the program's starting point is, and so on.  To run or modify a program using Eclipse, the first thing to do is to start up Eclipse and then create a new project or open an existing project to contain and keep track of our classes.

Let's start by creating a very simple program with a single class. To keep things simple, the only method we will create is a main method.

• Start up Eclipse.    If you get a "Workspace Launcher" dialog box, click on the Browse button and create a new folder with a name such as EclipseWorkspace.
• Create a new project.  In the Eclipse "File" menu, move the mouse to the "New" menu item.  In the pop-up submenu that appears, select "Project."
  • A new window will appear. Make sure that "Java Project" is selected.  Click on the "Next>" button. 
  • Give your project a name, such as Lab1, Simple Project, Experiment, or some such name.  Click on the "Create project from existing source" checkbox. For the location, you want to specify your own directory.  Click on the "Browse" button to do this. 
  • In the pop-up window that appears, click on the plus sign next to "My Computer" and then choose your directory on the campus server (or click on the plus sign next to your directory and choose the folder you created for this course).  Click on the "New Folder" button to create a new folder for this project.  Without clicking anywhere, type in a new name for the folder.  (If this doesn't change the folder's name in the navigation pane, click on the "New Folder" label until the name appears in a box with a cursor; then type in the new name.)   Click on the "OK" button.
  • Don't bother with the "Next>" button, just click on the "Finish" button.  If you get a dialog box asking about the Java Perspective, just click "Yes."
  • You should see a folder with the name of your new project appear in the "Package Explorer" pane on the left side of the Eclipse window.
• Create a new class.  In the Eclipse "File" menu, move the mouse to the "New" menu item.  In the pop-up submenu that appears, select "Class."
  • A new window asking for information about your new class will appear.   You don't have to worry about most of the fields in this window, just choose a name for your class (such as SimpleClass or something along those lines) and then click on the public static void main checkbox (one of a set near the bottom of the window).  Also click on the generate comments checkbox at the bottom of the window.   Then click on the "Finish" button.
  • You should see an icon labeled "(default package)" with another icon for your new class appear under the folder for your project in the "Package Explorer" pane on the left of your Eclipse window.
• Edit the new class.  You should notice the tab above the central editing pane in your Eclipse window labeled with the name of your new class. 
  • When there is more than one file active you can click on each tab to move to the other files.  By clicking on the "X" that appears on the tab when that tab is selected; you can close that file. 
  • Scroll up and down in your class.  Notice that there are two sets of comments about your class.  The first set, preceded by "//" on each line, will contain basic information about the name of the class, who created it, and how it has been modified.  The second set, enclosed in "/** ... */" comment markers, will describe what assignment this class was created for, what the purpose of the class is, and, again, who created the class.  This is a special "javadoc" comment that could be used by the "javadoc" tool to create an HTML file with documentation about your class.  If these comments don't exist already, add them.  
  • Edit the "javadoc" comments for your new class.  Change the one-sentence description to indicate that this is a test class to experiment with creating a new class in a new project.  Delete the sentence saying "A more detailed description goes here..." (unless you want to replace it with a more detailed description of your class).  Either edit or delete the second @author line, depending on whether you are working with a partner or individually.
• Run your new program.  In the Eclipse "Run" menu, move the mouse to the "Run As" menu item.  In the pop-up submenu that appears, select "Java Application." If you haven't saved your modified file yet, you will be prompted to do so. You may see a quick task bar as the program compiles, but then you won't see anything interesting, because your program doesn't actually do anything.  Yet.
• Edit and run again.  Find the line of code that says "public static void main(String[] args)".  Don't worry about the fact that this line of code doesn't mean anything to you now -- we will learn about it soon. Move the mouse to the right of the open brace ("{") after the "public static void main" line.  Hit the Enter key.  You should see a new line open up, and the mouse should be indented about 4 spaces in from the open brace.  Type

      System.out.println("Hi");

  Notice that the Eclipse editor is trying to be smart.  As soon as you type in the left parenthesis and double-quote mark, it will add the right parenthesis and second quote mark.  If you type the second quote mark and then the right parenthesis yourself, it will just move over the characters it added for you.  Alternatively, you can use the mouse or arrow keys to move past the characters it added.   Now you can run your program again as you did above, or you can click on the icon of a green circle with a white triangle (beneath and between the "Refactor" and the "Navigate" menus). This time you should see the word "Hi" appear in the Console pane beneath your class.
• Creating documentation for your program. In the Eclipse "Project" menu, move the mouse to the "Generate Javadoc..." menu item. In the pop-up window that appears, go to the "Javadoc command" prompt, and navigate to, and select, "C:\ProgramFiles\Java\jdk1.6.0_13\bin\javadoc".  Then click on the "Finish" button. If a dialog box appears, click on the "OK" button. Eclipse will generate the documentation - the console window will show your progress. When the word "terminated" appears next to the word "Console" on the Console window, the documentation generation is complete. In the Navigator pane, click on the plus sign next to the folder "doc" and then double click on the file index.html. This will bring up your documentation in a browser tab within Eclipse. Explore the documentation that has been generated. The documentation for this program is not very interesting but it does show you how easy it is to create documentation that matches your program comments. When you are finished exploring, click on the "X" at the top of this tab to close this browser. We will use the "javadoc" tool again later in the quarter.
• Click on the "X" on the tab for your class to close that file.

Exercise 2: Importing an Existing Project Using Eclipse

For this part of the lab, you will copy and run an existing project.

• Go to the web page for the upcoming GridIterator Lab.  Download the zip file containing the project code, and unzip the folder someplace on your M: drive.
• Start up Eclipse if it isn't already running.
• Select "Import" in the Eclipse "File" menu.
• In the window that appears, choose "Existing Project into Workspace" and then click on the "Next>" button.
• Click on the "Browse" button and navigate to the "GridIterator" folder in your directory on the campus server.
• You should see a folder labeled "GridIterator" appear in the "Package Explorer" pane on the left side of the Eclipse window.  
• Run the application by right clicking the GridIterator folder and selecting "Run-As->Java Application".

Exercise 3: Refactoring and the Edit-Compile-Run Cycle

Now let's return to a project you were working on before, to add new functionality to it.  You will do this frequently in this course, since enhancing an existing program (editing, compiling, and testing existing files) is much more common than creating a completely new one.  In fact, since it is almost impossible to sit down and write a program absolutely correctly from scratch, even new programs are often created by modifying previous programs.

• In the Package Explorer pane, select the project you created in Exercise 1 above.  If you can't see the class you created indented below the project, click on the plus sign next to the project folder.  (You might need to click on a plus sign next to the "(default package)" icon also.)  Click (or double-click, if necessary) the class you created.  You should see it appear in the central editing pane.
• Now let's edit and personalize the program. Scroll down to the System.out.println statement you added earlier.  Replace the string between the double quotes to make the program print out "Hello, your name" instead. Run it again. Did you get what you expected? If not, fix it!
• The name you chose earlier for your class is probably not very descriptive.  Change its name to a more descriptive name for this class.  The name should start with a capital letter, since this is the convention for class names in Java.  Eclipse provides an easy way to change the class's name in a consistent way.
  • Select the class in the Package Explorer pane.
  • In the Refactor menu, choose "Rename."
  • In the dialog box that appears, enter the new name.  Mark the checkbox so that any references to the class name in your code or in comments will be changed as well.
  • Click on the "Preview" button.  If your class contains a "main" method, you may get a warning about other classes that might use this one.  You can just click on "Continue" to proceed.  You will get another pop-up window informing you of what changes are to be performed.  Click on "OK".
  Note that the name of the class in the Package Explorer pane changed.  Scroll through the class to make sure that other necessary changes were made also.  Update the class description in the "javadoc" comments.
• You can also give the project a more meaningful name. Select the project name in the Package Explorer pane and then choose Rename in the Refactor menu.  After doing this, you may need to click on the plus sign next to the project name to open it up and see its contents.
• You should also change the name of the directory containing your project, to make it easier to find next time.  Select your project in the Package Explorer pane and then choose "Move" in the Refactor menu.  In the dialog box that appears, change the name of the directory (the last segment of the Location name) to the same name as your project.  Click on the "OK" button.

Exercise 4: Creating a New Project from Existing Source + Using JavaDocs

Download and unzip the file WordAnimation.zip to your M: drive.  

• Create a new project as you did in Exercise 1 above. 
• Expand your new project in the Package Explorer, and right click on the "src" icon.  Select "Import..."
• Expand the "General" folder and select "File System".  Press "Next". 
• Browse to the folder where you created when you unzipped the file above.  
• Check the boxes associated with the .java files and click OK. 
• Right click the project, and follow the same procedure to import the file "alice.txt".  Since that is not a Java file, you don't want to import it into the "src" folder. 
• Run the project. 
• If you have time, modify the project so that every word is assigned a random color: (You will need to make use of the Java 6 API)
• Add an instance field to the MovingWord class to store a color (of type java.awt.Color)
• Modify the MovingWord constructor so that it selects a random color ( You will need to create an object of type java.util.Random, and use its getNextInt method.)
• Modify the Draw method of the MovingWord class so that it uses the appropriate color.  (You may want to look at the documentation for the java.awt.Graphics2D class.)