Eclipse is a free open-source Java environment available from Eclipse is a Java program, but it uses a custom user interface toolkit that does not run on all platforms that supports Java 2. Check the web site for supported platforms. Eclipse requires a Java 2 runtime, so you need to install the Java 2 SDK first before installing Eclipse. You can download the SDK from For this course, you will want the J2SE 1.4.2 release. (If you have a Macintosh, the Java 2 SDK is already installed)

Starting Eclipse

When you start Eclipse, a startup screen appears, and the program spends some time loading various modules.


Eclipse will ask you for your workspace (where on your computer the projects you are working on will be stored.) The prompt will look like the following: Click on the Browse... button to navigate to the directory of your choice if it is not already selected or in the drop-down menu...

Workspace Prompt

When Eclipse has finished loading, you see a screen similar to the following:


Loading an existing program

If you already have your program in project workspace (see above), but it is not in the Package Hierarchy window on the left of the screen, then you need to make a project that contains the file(s). Follow these steps.

Select File->New->Project from the menu. You will get the following dialog.


Select the Java Project option and click on the Next > button. (Do not select the Simple option!)

In the following dialog, give a name to the project, the same name as the directory that contains the files (watch spelling and capitalization). There should be a message indicating  The specified external location already exists. Eclipse will then  attempt to import all the resources available at that location. Check Create project in workspace if it has not been selected.


Click on the Finish button.

The project appears in the left hand panel. Expand it, and also expand the default package icon. Double-click on one of the file names. The file is displayed in an edit window:


Starting a new program

If you write a program from scratch, then you can start your work in Eclipse. It is always best to place each of your programs into a separate directory.  Eclipse will create the directory for you.

Select File->New->Project from the menu. You will get the New Project dialog.

Select the Java option and click on the Next> button. (Do not select the Simple option!)

In the following dialog, give a name to the project. Accept the default choices, Create project in workspace and Use project folder as root for sources and class files


Click on the Finish button. Now locate the name of your new project in the left hand panel. Click on it with the right mouse button (Windows) or control-click (Macintosh). Select New->Class from the context menu

The New Class dialog appears.

Supply the name of the class. If you want a main method for this class, check the box public static void main(String[] args).


Click on the Finish button.

Finally, you get an editor window into which you can type your program.


As you type in your program, occasionally select File->Save from the menu to save your work.

You may enjoy the "content assist" feature of Eclipse. If you type a partial input and then hit CTRL+SPACE, a dialog shows all possible completions. Just pick the one you want from the list.


You may also want to experiment with some of the other convenience features of Eclipse, such as Source->Generate getter and setter.

Finding Errors

Eclipse continually compiles (attempts to convert your source code into byte-code for the machine), so the Editor will display problems in your program. (See the red X in the leftmost column in the editor window below.)

By double-clicking on the red X, a description of the problem and some helpful options are displayed. In this case, you would click on Change to 'System' (java.lang)


Running a program

To run a program, right-click (Windows) or control-click (Macintosh) on the file with the main method, and from the context menu select the Run->Java Application menu option. The program runs. Any console output is directed to a window at the bottom of the screen.


Running applets

To run an applet, make sure the current project is still selected in the leftmost pane. Then select the menu option Run->Java Applet. Eclipse will launch the applet viewer on the subclass of Applet that it finds in your project.


The applet viewer is started with a default size which is rather small. Just resize the applet window.

Close the window to terminate the applet.

Generating Javadoc comments

Select Project -> Generate Javadoc from the menu. You will get a dialog such as the following one:


Click the cleckbox for the project that you want to document. Then make sure that the destination directory is correct. Click on Finish.

Tracing through a program.

Before debugging a program, you should set a breakpoint at the start of the main method.

Double-click on the gray bar to the left of the edit window, next to the first source line after the line public static void main(String[] args). A blue dot appears, indicating the breakpoint.


Then select the menu option Run->Debug as...->Java Application. The debugger starts and switches the Eclipse display to the debugger perspective. It pauses at the breakpoint that you set.


Whenever you select the menu option Run->Step Over (or the F6 keyboard shortcut), then the debugger executes one line of the program, without stepping inside method calls. For example, tracing over the call

Word w = new Word(token);

will not trace inside the Word constructor but simply run the program to the next line of the main method.

Contrast that with the menu option Run->Step Into(or the F5 keyboard shortcut). This command traces inside method calls. For example, tracing into the line

int syllables = w.countSyllables();

stops at the first line of the countSyllables method:


Watching values

To see the value of a variable of a simple type (such as a number or a string), simply hold the mouse pointer over the variable name when the debugger is stopped. Then the contents of the variable is displayed in a small rectangle next to the variable name. For example, here is the contents of the count variable in the countSyllables method.


The top right window shows all local variables. Click on the triangles to look inside objects. To see the instance fields of the implicit parameter, look inside this.


The top left window shows the call stack (with the most recently called method on top). For example, the following call stack shows that the WordTest.main method called the Word.<init> method, that is, the constructor.


Setting breakpoints

Tracing through a program can be tedious. Often, you want the program to run at full speed until a particular line of code is encountered. To set a breakpoint at a line, double-click on the gray bar to the left. A blue dot indicates the breakpoint.


Now select the menu option Run->Resume or hit the F8 keyboard shortcut. The program runs to the next breakpoint, stopping only for user input.

You can set as many breakpoints as you like.

To remove a breakpoint, double-click on it with the mouse.

Stopping the debugger

When the program has completed, the debugger stops automatically. When you want to terminate a debugging session without running the program to the end, select the menu option Run->Terminate.

To return to the Java perspective (in which you can edit and compile your program), locate the perspectives toolbar at the left of the Eclipse frame:


Click on the button with the "J" (above the bug button). Eclipse will remove the debugger windows and restore the edit windows.