Deleting a Class

Importing Files

File System Import

The contents of a Java project are defined by the contents of the folder in your filesystem in which the project is stored. What happens if you want to grab a Java file from some other location and make it part of your current project? This process is called importing and can be done simply with Eclipse: simply right click on the Project in the package explorer and select "Import". This will bring up an Import window that has a couple of options to choose. The two relevant ones are "File System" and "Zip File". If you choose "File System", you can import any Java file from anywhere else on your local file system (i.e., your computer). So you could use this option to pull in a Java file from a directory other than the one you're using for your current Java project. This can be accomplished by first selecting the directory from which you want to import the Java files by either filling in the edit box at the top of the Import window or by selecting it with the "Browse" button. After doing so, you'll see the directory appear in the window on the left. Next to the folder name you'll see a square box that you can check and uncheck. Checking the box means "import everything in that directory". When you click on the directory name, the right window will display all of the files in that directory. Each file will have a similiar checkbox. Each file that is checked will be imported into your project.  Importing files into your project will cause copies to be created of the files you're importing. Thus, once your import a file, a copy of that file will be created and put in your project's directory. Changing the file you've imported will not change the original source file, and vice versa. Deleting a file you've imported from your project will not delete the original file.

Zip (jar) File Import

If you want to import a jar file, you'll want to select your project, right click and choose "Import", but instead choose "Zip file". The options here are very similiar to when importing from the file system, since a Zip/Jar is really a miniature file system stored in a single file. After you choose the Jar file you want to import from, you'll see a directory structure with checkboxes that behaves just like when importing from the file system. Check the folders or individual files you want to import and select "Finish." Again, copies of the contents of the Jar file are made, so you can safely manipulate the files and delete them without affecting the source Jar file.

Exporting Files

This time, we're going to be creating a copy of our project somewhere else. Right click on the project and select "Export". You'll see a list of options similiar to the list for importing files, and again the relevant options are "File System" and "JAR file". This time, the left and right windows show you the contents of your current project. Checking and unchecking items here selects which files in your project you want to export. If you choose "File System", you simply specify the folder where you want to copy your project files and hit "Finish".

Creating a Jar File

Creating a JAR file is slightly more complicated. JAR files can contain either compiled code, source code, or both. By default, Eclipse assumes you're exporting compiled code, so it only lists .class files and other files required by the compiled code. To change this, modify the checkboxes right below the folder/file windows so that "Export generated class files and resources" is unchecked and "Export java source files and resources" is checked. If you are submitting a project via a JAR file and you forget to do this, you will not provide your .java files.  Make sure you export your Java source files if what you want to provide is your source code.  Once that is straightened out, choose a location for your JAR file and then hit "Finish". You can test whether or not your JAR file worked by creating a new Project and importing your JAR file into that new project as described above. If the new project you created looks just like your original project, chances are your export worked correctly.

Displaying Line Numbers in the Editor 

You'll probably find it useful to display line numbers in your code editor. When an error occurs in your code, the Java VM will tell you what line number in the source code it occurred on. You can find that line quickly if your line numbers are displayed. In order to do this, select Window -> Preferences on the main menu, which will bring up the Eclipse options, where you can set your preferences (things like font size/color, etc). On the left there is a list of categories. Click the '+' next to "Java" to expand that category, and select "Editor". The right window will be populated with a group of tab panes. You want to select the "Appearance" tab (it is selected by default). Check the second checkbox ("Show line numbers") and hit "OK". You should see line numbers appear in your editor (if you have a Java file open). 

Renaming Projects, Classes, Files and Variables

To change the name of a project, class, file, variable or method highlight the item and select "Refractor"->"Rename".  You will then be prompted to enter a new name.  Hit "OK" and you are done.

Searching in a Java File

IIf you are editing a Java file and you want to locate a specific phrase somewhere in your code, you can use Eclipse's search tool. Eclipse has a more advanced searching mechanism than most Windows applications. Select Search -> Search. This will bring up the search window, which has a series of tabs. To use a standard phrase-based search, select the first tab and enter a search string, and hit search. The search results will be displayed at the bottom of the screen. Double clicking on the results listed will focus the editor on that instance of the search string. These searching utilities makes it easy to quickly locate anything in your project, so experiment with the search tool -- it can save you a lot of time later.

Interactions Pane

The interactions pane is part of the Dr. Java perspective and appears as a tab pane along with "Console". The interactions pane is basically a command interpreter that feeds Java code into a running JVM, which means you can use it to test a statement, or series of statements, in Java code.  The Dr. Java perspective allows you to practice different constructs of the language without having to write a full class.  For example, if you want to verify how perform String manipulation in Java, you could write the following statements in the Interactions Pane which will process the statements for you:

In addition to creating standard Java objects, you can also create instances of objects you've defined in your project. For example, let's say your project has a Foo class. After you compile your project, you can type Foo f = new Foo() in the interactions pane and experiment with your own code.