IntelliJ IDEA suggests several ways to close editor tabs.

To close a file in the editor, do one of the following
  • On the main menu point to Window | Editor Tabs, choose one of the appropriate closing commands.
    Close
    Closes the file in the active tab.
    Close All
    Closes all editor tabs.
    Close Others
    Closes all tabs except the current one. The alternative way to close all other tabs lays with clicking the close1 button, while holding the ⌥ key pressed:

    close_others

    Close Unmodified
    Closes all files that were not changed. This command is only available, when version control integration is enabled in project.
    Close All But Pinned
    Closes all files that were not pinned. This command appears, if there are pinned editor tabs.
  • Right-click any editor tab, and choose same commands on the context menu.
  • Point with your mouse cursor to a tab and click the middle mouse button.
  • Point with your mouse cursor to a tab and click close1.
  • Press ⌘W or ⌘W⌘F4 or ⌘F4⌘W or ⌘W^ F4, ⌃F4 or ⌃F4^ F4, ^ X, K, ^ X, 0, ⌃F4, ⌃X, K, ⌃X, 0, ⌃F4, ⌃X, K or ⌃X, 0.

When you close modified files, IntelliJ IDEA preserves all changes in the current editing session. After reopening such files, the results of editing are restored.