Step 3: How to edit a project
This step will show you how to edit a source file in Eclipse.
You're almost there! The next step will be to run the program.
Launch the Eclipse IDE if it is not currently running. Return to Step 1 of this tutorial if you
need help completing this step.
- We need to create a source file where we will write our program.
Right-click on the "HelloWorld" project in the Package Explorer tabbed
pane on the left side of the screen and navigate to New → Class,
as in the following example:
- Another window will be displayed. Then click in the text box labeled
"Name:" and type in HelloWorld, as in the following
Click Finish. This step will create a new file named HelloWorld.java and
add it to the project for you. It will also open a tabbed window where you can
edit the HelloWorld.java source file.
- Now that we've completed the setup we can write the program.
Enter the following text into the HelloWorld.java window.
As you edit the file, you may notice red underlines appearing.
This is Eclipse's attempt to correct you, the same way a word
processor attempts to correct spelling. If you follow the above, the
red lines will eventually disappear, though it is normal for some to
appear as you are writing programs. If there are still some left,
compare the above image with the file you wrote until you find the
difference. You can align the braces as shown in the code examples
in the textbook or align them as shown in the code above. The difference with the code
above will not cause
Also, note that even if the red lines disappear, this doesn't mean
that your program will work correctly! Just as your word processor
only knows how to spell and the rudiments of grammar but not how to
write an essay, Eclipse knows what a valid Java program looks like,
but doesn't understand whether or not the program you wrote does what
you want it to. For a simple program like the above, it may very well
work as soon as it is recognized as a valid Java program, but for more
complicated programs, validity is only the tip of the iceberg.
It's also worth mentioning that Eclipse will fill things in for
you. For example, if you put a left parenthesis (, it will
follow it up with a right parenthesis ). You can keep on
typing and fill in the space between the parentheses. When you're
done, you can either manually type the end parenthesis ),
which will type over the old one, or you can press the right arrow key
to skip past the old one.
- Finally, personalize the file by adding the following header to
the top of the file and fill in the fields appropriately. The Title
is the name of the overall program (HelloWorld in this case)
and Files is the list of source files you created (just
HelloWorld.java in this case). This header should be
included with all of the files you hand in. Instead of typing the
header yourself you can select (click and drag over the text) the text
below and choose "Copy" from the "Edit" menu, or hold Ctrl and press C
on your keyboard. Then put the insertion point at the top of your
HelloWorld.java file and choose "Paste" from the "Edit" menu,
or hold Ctrl and press V on your keyboard.
// ALL STUDENTS COMPLETE THESE SECTIONS
// Title: (program's title)
// Files: (list of source files)
// Semester: Fall 2012
// Author: (your name and email address)
// CS Login: (your login name)
// Lecturer's Name: (name of your lecturer)
// Lab Section: (your lab section number)
// PAIR PROGRAMMERS COMPLETE THIS SECTION
// Pair Partner: (name of your pair programming partner)
// CS Login: (partner's login name)
// Lecturer's Name: (name of your partner's lecturer)
// Lab Section: (your partner's lab section number)
// STUDENTS WHO GET HELP FROM ANYONE OTHER THAN THEIR PARTNER
// Credits: (list anyone who helped you write your program)
//////////////////////////// 80 columns wide //////////////////////////////////
While you are editing the source code, it is a good idea to save your work
frequently. The more often you save your work, the less work you will have
to recreate in the event of a system crash or other interruption in your
You save the file by clicking on the disk icon. Files that have
been modified since last save will have an asterisk before the file
name, as in the above image.
Original version created by Deb Deppeler and Sue Hazlett
Updated for Eclipse by Martin Hock
Updated for lab section use by Beck Hasti
2010-2012 Updated by Jim Skrentny