6. Using Git in an IDE¶

Start IntelliJ and create a new Java project called vctest. Then create a class called Hello, containing a simple “Hello World” program:

public class Hello {
  public static void main(String[] args) {
    System.out.println("Hello World!");
  }
}

Before going any further, you need to set up a .gitignore file, to tell Git which files and directories should not be put under version control. Put this in the vctest directory.

.idea/
out/
*.iml

Choose VCS ‣ Enable Version Control Integration… from the menus at the top of the window. Select Git as the version control system on the resulting dialog and click OK.

IntelliJ will create a Git repository in your project directory, and the Version Control tool window will become available. Activate it now by clicking on the tab or pressing Alt+9. Depending on your .gitignore, you should see two or more unversioned files listed in the Version Control tool window, highlighted in red [1]. The same highlighting is used when listing the files in the Project tool window.

You can perform a git add operation on individual files by right-clicking on them and choosing Git ‣ Add or by selecting them and pressing Ctrl+Alt+A.

To add multiple files, you can Shift- or Ctrl-click to select the ones you want in the Version Control tool window and then either right-click and choose Add to VCS or simply press Ctrl+Alt+A. If you want to add everything, it is easier just to right-click on the project directory and use the same menu option or keyboard shortcut.

Do this now for your project. You should find that the files are now highlighted in green - signifying that additions have been staged but not yet committed.

You can commit the changes in various ways. For example, you can right-click on the project folder and choose Git ‣ Commit Directory; alternatively, you do this in the Version Control tool window, by right-clicking on the ‘Default’ heading in the Local Changes panel and choosing the Commit Changes… option, or by selecting ‘Default’ and then clicking on the Commit Changes button (the one with ‘VCS’ and a green arrow pointing upwards) in the vertical toolbar at the left.

Use one of these methods now. The Commit Changes dialog will appear, allowing you to review in detail all the changes that will be committed. Notice the options under ‘Before Commit’ on the right. IntelliJ can reformat code to match the coding style defined for the project and perform various clean-up operations before committing, if you want it to.

Enter “Initial version of program” as the commit message and then click the Commit button at the bottom-right of the dialog to finalize the commit. After a brief delay, you should see all of the changes disappear from the Local Changes section of the Version Control tool window.

Now make a change to Hello.java. Change the printed message from “Hello World!” to “Hi there!”. Notice that Hello.java reappears in the Local Changes panel of the Version Control window. Notice also that the file is coloured blue, both there and in the Project tool window. This is how IntelliJ highlights changed files (as opposed to untracked files, which are coloured red).

To view precisely what has changed, click the Preview Diff button in the Version Control tool window. You’ll find this near the bottom of the second column of buttons on the left, just above the Help button. Click the button again to hide the diff.

Now let’s try a different way of accessing version control operations. Choose VCS ‣ VCS Operations Popup… from the main menu and a pop-up menu of useful operations will appear. Notice the options to commit all changes or commit just the currently-selected file.

Use the pop-up menu or the Ctrl+K shortcut to commit the change that you’ve made to Hello.java. When the Commit Changes dialog appears, expand the section at the bottom so that you can see the diff for the changed file. Then enter “Changed greeting” as the commit message and click Commit.

Finally, click on the Log tab of the Version Control tool window. You should see the two commits listed. You can click on a commit to see further details. The changed files are listed on the right and you can use the buttons above the list of files to interact with the list - e.g., to view the diff for the selected file in a separate window.

Use a web browser to log in to your GitLab account and create a new project called vctest.

Return to your vctest IntelliJ project and choose VCS ‣ Git ‣ Push. On the resulting Push Commits dialog, click the ‘Define remote’ link and specify the SSH or HTTPS address for the vctest GitLab project [2], then click OK.

Back on the Push Commit dialog, click the Push button. Authenticate with your SSH passphrase or GitLab account credentials (as appropriate) if prompted. IntelliJ will notify you whether the push succeeded or not.

If the push succeeded, return to gitlab.com in your web browser and refresh the page for the vctest project. The two commits that you made earlier should now be visible.

Make another change to Hello.java, then bring up the Commit Changes dialog. Write an appropriate commit message, then hover the cursor over the Commit button at the bottom-right. Notice that you now have two options: commit locally, or commit and then push. Try using the latter.