IntelliJ IDEA User Guide. Pop-up windows with hints.

Tooltips (windows)

Всплывающие подсказки (окна) полезны для проверки дополнительной информации относящейся к элементу на котором установлен курсор. Приведем список всплывающих подсказок, которые помогут вам повысить производительность труда.

Parameter Information Information about the parameters required for a particular method is available by pressing Ctrl + P (Cmd + P) . A popup window shows the appropriate overloaded method, highlighting the current parameter.
Quick description If you want to quickly look at the implementation of the method on which the cursor is placed, you can call up a quick description by pressing Shift + Ctrl + I (Shift + Cmd + I)
Documentation The documentation pop-up window is one of the most commonly used. To open it, press Ctrl + Q (Ctrl + J on Mac) .
"Non-disappearing" tooltip (window) If you have already opened the documentation and want to keep the documentation open, click on the Pin button in the upper right corner. The documentation for the current item will be shown (and will not disappear).
Windows that pop up from the panel If you are not satisfied with “floating” windows, you can attach them to the edge of the main window by clicking on the button in the upper right corner.
Popup Windows in Other Components of the Development Environment It is well known that tooltip popups can be triggered for any code element in your editor. However, they are also available for items in any other list, using the same keyboard shortcuts.
You can trigger tooltips even when you navigate through items in the navigation bar by pressing Alt + Home (Alt + ↖ for Mac) .
“Show Usage Locations” “Show Usage Locations” is a very simple yet powerful feature. Just press Alt + Ctrl + F7 (Alt + Cmd + F7 for Mac) and you will see a list of places in your code where the element (method or object) under the cursor is used.

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