COMP 310

Using the Eclipse Integrated Development Environment

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Eclipse has a notion of "perspectives" which are collections of panels and tabs that form a graphical user interface specifically geared towards a particular type of task.   There are perspectives for editing and compiling Java programs ("Java" perspective), for working with source control ("SVN Respository Exploring" and "Team Synchronization" perspectives), for debugging and a variety of other tasks.

To open a particular perspective you can go to either Window/Open Perspective on the main Eclipse menu bar, or click the "Open Perspective" icon at the upper right corner of the Eclipse window.    In that same upper right corner will be icons to quickly switch from one perspective to another.

The most common perspectives to use will be "Java" and "SVN Repository Exploring".

Always make sure you are in the proper perspective for the task you are atempting!

Workspaces and Projects

A workspace is a directory that holds one or more Eclipse projects.   Workspaces can be used to organize multiple projects.  It is highly recommended that one at least have a workspace for Comp310 and possibly individual workspaces for sets of projects, such as the Ballworld series.

An Eclipse project holds all files associated with a particular Java application.   All work should be done as part of a project.  The source and compiled (class) files in a project should be always be separated into "src" and "bin" folders.   

Creating a New Project

  1. Be sure that the perspective is set to "Java".
  2.  On the main Eclipse menu, click on File/New/Java Project.
  3. Be sure the following options are selected (they should be the defaults):

By default a project directory will be created in the workspace and separate  "src" and "bin" folders created below it to hold the source code and class files respectively.

Creating a New Project from Existing Code

  1. Create folder in the desired workspace folder to hold the project.  It is recommended that you name of the folder should be the same as you wish for the project itself.
  2. Create a sub-folder called "src" in the project folder and copy all the Java code into it such that src is the default package directory for the code.   Thus all packages defined in the code should be sub-folders of src.
  3. In Eclipse, be sure that you are in the desired workpace, then go to File/New/Java Project.
  4. In the New Java Project dialog window, select Create project from existing source and then select the Directory by browsing to the project directory you made above.
  5. Be sure that Create separate folders for sources and class files is selected (should be the default) and then click Next.
  6. In the Java Settings dialog, under the "Source" tab, select the "src" directory that you created above.   Be sure that "Default output folder" is set to something like "[project name]\classes". Click Finish.

Creating a New Package, Class or Interface

To create a new package:

  1. In the Package Explorer pane on the left side of the Java perspective, right-click on the location where you want your new package, typically the src folder or an existing package folder, OR highlight the desired package location and then click the New Package icon on the top icon bar.
  2. On the pop-up menu, select New/Package.
  3. Complete the fully-qualified name of the new package, e.g mySuperPackage.mySubPackage1.subSubPackage., and click Finish.

To create a new class or interface:

  1. In the Package Explorer pane, right-click on the package where you want your new class or interface OR highlight the desired package location and then click the New Class or New Interface icon on the top icon bar.   You may need to pull a drop menu down to see the desired icon.
  2. In the pop-up dialog, fill out the desired name and other properties of the new class.   Eclipse can auto-generate method stubs of inherited abstract methods for you, saving you some error-prone typing.
  3. Click on Finish when you are ready to create the class file.

The "Enclosing type" option is for when you wish to create a named inner or nested (static) class inside an existing class.

WARNING!  Eclipse and Subclipse do not properly interact when moving and renaming packages and folders!   Follow the these directions carefully.

Renaming or Moving Files

To rename or move a file in Eclipse, use the built-in refactoring tool:

  1. Right-click the desired file and select Refactor...
  2. To rename the file, select Rename
  3. To move the file, select Move

NEVER use the straight "Rename" option in Eclipse or move a file by drag-and-dropping it as this may break references to the file.   ALWAYS USE REFACTOR!    Refactoring will preserve most references to the file and thus is much safer.

NEVER manipulate files directly in the source control repository!    This will almost definitely generate "file out of date" errors.

Deleting a File

To delete a file, be sure you are in the Java Perspective.

NEVER delete a file from the SVN Exploring Perspective!     This will cause "file out of date" errors.

  1. If you are under source-control, do a commit to ensure that the local copies are in sync with the repository.
  2. Right-click the desired file and select "Delete".
  3. If under source control, perform another commit to re-sync with the repository.


Compiling and Running a Program

When you attempt to run your program, Eclipse will automatically compile the code first.  

To run your program for the first time:

  1. In the Package Explorer, highlight the class that contains the main() method that you wish to use to start your application.
  2. Click the green VCR-like "Run" button on the top icon bar.

Running your application using the above procedure will automatically create a "launch configuration" that Eclipse will use in the future to run your application.  You can edit the specifics of a launch configuration (see below).

To run your application once a launch configuration has been created:


Compiling Without Running:

Sometime you want to compile the code without running it, just to check for errors.   There are a number of options, all available under the main Eclipse "Project" menu:


Working with Compilation Errors and Warnings

Alas, compilation errors and warnings are a fact of life.   Eclipse makes life a little easier by enabling one to more quickly track down and fix compiler errors and warnings.

Compiler errors and warnings appear in the "Problems" tab at the bottom of the Java perspective.   If the Problems tab is not visible, go to "Windows/Show View/Problems"  on the main Eclipse menu.   Note that errors and warnings may not appear in the Problems tab until the file has been saved.


Including a JAR file

Java ARchive files are special zip files that the Java system uses to bundle up entire code directory hierarchies into an single file for easy deployment.   JAR files are very useful for adding libraries of code to your project without having to add a huge package directory structure to your system.   Instead, the packages for a library are putinside of a JAR file, which is simply included in your project.  

Conceptually, what Java (and Eclipse) will do is to unzip the JAR file and attach it to the default package of the project. Thus, any packages in the JAR are available for use as if you had manually unzipped to JAR and put all the internal packages in their respective locations in your project.

If you have a JAR file with  a library of packages that you wish to include with and be able to access from your project, you need to include it in the Java "Build Path":

  1. Rick-click the project and select Properties (at the bottom of the menu).
  2. Select "Java Build Path"
  3. Select the "Libraries" tab
  4. Click "Add JARs..."
  5. Browse to the JAR file you wish to include.
  6. Click OK to confirm your selection and close the Add JAR dialog.
  7. Click OK to close the Properties dialog.


Exporting Javadocs

JAVA DOCuments are web pages (HTML files) that Java can automatically generate from Javadoc-compliant code comments.   The ability to automatically generate easily readable documentation directly from the code files was a major advancement in software development technology when it came out.

Eclipse can easily create Javadoc web pages through its "Export" capabilities:

  1. Highlight the project for which you wish to generate documentation web pages.
  2. On the main Eclipse menu, select File/Export...
  3. In the Export dialog that comes up, select Java/Javadoc then click Next.
  4. In the Javadoc Generation dialog that comes up, set the following options:
    1. Javadoc command: If this is your first time to export Javadocs, this field may be blank.
      1. Click the Configure... button 
      2. Browse to the location of the javadoc executable which is generally located in the bin subdirectory of the Java JDK installation directory. Here are some typical locations for the javadoc executable on different systems:
        • Windows:  C:\Program Files\Java\jdk1.6.0_21\bin\javadoc.exe  (exact directory name depends on the version of the JDK installed)
        • Mac:  Separately, open a command window and type "which javadoc".  This will tell you the location of the javadoc executable.
        • Linux: Separately, open a command window and type "which javadoc".  This will tell you the location of the javadoc executable.   On Ubuntu, a typical executable is   /usr/bin/javadoc.
      3. Highlight the javadoc executable and click Open.
    2. Select types for which Javadoc will be generated:  Be sure that the project that you want to generate documentation for is checked, and only that project.
    3. Generate Javadoc for memebers with visibility:  Select Private.
    4. Use standard doclet:  Checked -- generate standard HTML documentation files.
    5. Destination: Click Browse... and navigate to your project directory.   Just below your project directory, create  a "doc" directory (same level as "src" and "bin"), highlight the doc directory and click OK.
      • WARNING: If the path name to your javadoc output location includes spaces anywhere in the path, Eclipse may automatically replace the spaces with the URL-friendly "%20".    The symptom is that your javadocs will not appear in your desired location even though Eclipse indicates a successful generation process.   This is because the computer's operating system interpreted this new pathname as a different location than you intended and write your javadocs there. 
        • Solution: Check the full path that Eclipse sets for the ouput location and revert the auto-generated "%20"'s  back to spaces.   You can also just simply copy the incorrectly placed javadocs back to the desired location.
    6. Click Next to go to the next configuration window.
  5. In the next Javadoc Generation configuration window, set the following options:
    1. Document title: Enter a meaningful title that is pertinent to your project.
    2. Basic Options:  All boxes should be checked (default).
    3. Document these tags: All boxes should be checked (default).
    4. Select referenced archives and project to which links should be generated:  No boxes need to be checked (default).
    5.  Style sheet:  Unchecked (default).
    6. Click Finish as all the options in the next configuration window should be set to their defaults.
      • An Update Javadoc Location dialog may pop up.  Check that the location described is indeed where you want the javadocs to be located and click "Yes To All".
  6. A new tab will open in Eclipse showing the top level Javadoc web that was generated  (doc\index.html).   Browse through the Javadocs to make sure that what was generated matches what you thought you were generating!
  7. Commit your project to source control, being sure to include the doc directory.



Exporting JAR Files

Java ARchive files are special zip files that the Java system uses to bundle up entire code directory hierarchies into an single file for easy deployment. Instead of a whole messy and complex directory structure of files, all you need is a single file to run your application or applet.  Code and any required resource files, such as images or sound clips can all be bundled into JAR files.  The compiled class files are required to run the program but the source files can be optionally included as well.

To create a JAR file of your project from Eclipse, you need to "export" it.

  1. Click on File/Export...
  2. In the pop-up dialog window, select Java/JAR file as the export destination.  Click Next.
  3. Select the files you want to be in your JAR file.  Be sure that only the project you want is selected if you have multiple projects in your workspace.  You probably do NOT want any above the source directory, so be sure those files are unchecked.
  4. Slecte or type in the name and destination of the JAR file you wish to create.
  5. Be sure that "Export generated class files and resources" is checked off and optionally, "compress the contents of the JAR file".   Click Next.
  6. The default "JAR Packaging Options" are fine.  Click Next.
  7. Be sure that "Generate the manifest file" is checked.   Either option for sealing the JAR file is fine.  
  8. Specify the Main class by typing in or browsing to find the class with the main() method.   This is typically the controller in your MVC architecture.   This will enable you to run the application by using just the JAR file (double-clicking it or "java -jar MyJar.jar" for you command-line afficianados).  Click Finish to create the JAR file.


Problems Running Eclipse

"Out of Memory" or "GC Overhead Limit Exceeded" Errors

This sort error occurs when Eclipse is doing a memory intensive operation such as updating or creating a UML diagram and uses all of the memory the Java system has allocated for it.    64-bit versions of Eclipse seem to be particularly memory hungry, especially the newer versions such as "Luna".  To fix this error, one must modify Eclipse's start-up configuration:

  1. Close Eclipse if it is open.
  2. Go to Eclipse's installation folder, e.g. on a Windows machine, "c:\Program Files\eclipse"
  3. Using a text editor, open the eclipse.ini file.   Windows uses must start their text editor "as administrator" in order to re-save the file.
  4. Modify or add the "Xms" and "Xmx" parameters in the eclipse.ini file, by changing adding or modifying the values to be at least those below:

  5.  Save the eclipse.ini file and restart Eclipse.



Unable to Type Certain Characters

Sometimes, Eclipse gets into a weird state where you cannot type certain characters into one's code, seemingly as if that key was broken on one's keyboard.    For instance, a common occurance is that one can't type an asterisk (*) into one's code.  The odd part is that one can type those same characters into other parts of Eclipse and in other programs on one's computer so clearly the key on the keyboard is working just fine.  

What has happened is that somehow a "key binding" has been set for that key.   This is a "hot key" setting which is supposed to be a shortcut for a common Eclipse operation.     Typically, this is being set by a plugin when it installs but it seems that there must be some strange combination of key strokes that changes key bindings.


  1. In Eclipse, go to Preferences/General/Keys. You should see a big table of key bindings that maps Eclipse commands to particular key combinations.
  2. Click the "Binding" heading to sort the table by key bindings.
  3. Scroll down the table looking for key bindings (there may be more than one!) that start with the problematic key.   For instance, if you cannot type an asterisk, look for "Shift+8".    Note that the ky in question might be used in conjunction with another key, e.g. "Shift+8, I".
  4. Highlight the row with the key binding involving the key in question and click the "Unbind Command" button.    The binding value should be cleared out.
  5. Click "Apply" or "OK" to save the changes.
  6. Restart Eclipse to reset the key bindings to their new values (File/Restart).










© 2010 by Stephen Wong