Basic Eclipse User Guide.

Thanks to Don Slater at CMU for letting me use this page.

Important. Download and install Java first per these instructions then download and install the Eclipse IDE per these instructions.

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 JDK first before installing Eclipse. You can download the JAVA JDK from this web page. For this course, you will want the J2SE 8.x


Other sources: There are lots of good resources on the web for Eclipse. Here are a few good ones.

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:



Setting Eclipse to Java 1.8 (or later) Compiler

To ensure Eclipse understands the Java 1.8 features we will be using this term you need to set the compiler.

In the Eclipse main menu click on Window->Preferences... The preference window pops up. Select the Java category and expand it.

Click on the Compiler category to get the following window.

Set the Compiler compliance level to 1.8 from the pull down menu and then click okay.

Enabling Assertions on all your projects.

Assertions are statements in a program to about what the programmer believes to be true at a give point in execution. Assertions help to uncover logic errors. Assertions can be turned on and off. When off assertions are ignored by the compiler which doesn't do us much good during development. In this class assertions should always be on. To enable assertions follow these steps:

Select Window ->  Preferences.

The following window will appear.

Select and expand the Java option.

Select the Installed JREs option.

One JRE should be checked. Highlight that one and click the Edit button.

Under the Default VM Arguments: field type in -ea . This is a switch to enable assertions when Eclipse compiles you Java code.

Click the OK button.

Click the OK button in the preferences window. Assertions are now enabled and if an assertion is found to be false a runtime error will occur.

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.

Adding Existing Classes to A Project

You will often have to add preexisting classes to a project when doing assignments. Assume you have already created a project for an assignment. [See starting a new program above.] Download the source code files from the class web site to your computer. This example assume you have downloaded the files for Assignment 1 to the desktop.

The easiest thing to do is to simply drag and drop given Java program files into the src folder of your project. Choose the "Copy File" option in the dialog.

The long way if you are having trouble dragging and dropping files:

Ensure the project you want to add existing files to is open.

Right click on the project and select the import option from the pop up menu.

The import menu pops up. Select the file system option.

The Import File System Window pops up. Click the browse button and navigate to the folder that has the files you want to import.

 In this case it was the desktop. After selecting the directory that has the files click okay. The files in that directory are now displayed on the left hand side of the window.

Check the boxes of the files you want to import and then click finish.

The files selected have been copied into your project. Important! This copies the files into your project directory. Changes to the file in Eclipse are not reflected in the original files. When you turn in a file ensure it is the correct one!

Saving (exporting) a project in a different location for later use.

If you work in the lab you will want to save your work to a memory stick. When you logout of the lab computers all your work is erased from the machine.

To export an entire project right click on the project and select export.

In the pop up window that appears expand General, select File System, and then press the Next > button.

In the next window ensure your project is selected and then press the Browse button and browse to the location you want to save the project to, most likely a memory stick.

Click the OK button once you have the location you want.

Click the Finish button and the project will be saved.

Loading (importing) an entire project

When you go back to work on a project in the lab you can load a project from a memory stick.

Start Eclipse. Select File and then Import.

From the pop up window expand the General option, select Existing Projects into Workspace and click the Next > button.

In the next window select the Browse button and browse to the location of the project.

Find the project, select it, and then press the OK  button.

Click the Finish button and the project will be loaded into the Eclipse workspace. Be sure to export the project when you are done to save your changes.

Finding Errors

Even before compiling a program in Eclipse, the Editor can 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.

Displaying Line Numbers

To display line numbers in your programs select Window -> Preferences. In the pop up menu that appears expand the General menu. Under the expanded tree expand the Editors menu. Under the expanded tree select  Text Editors. Check the show line numbers box.