IntelliJ Idea IDE is the most popular IDE among Java Developers now-a-days. I use it for my day-to-day coding assignments. I use the following shortcuts quite heavily to improve my productivity while using IntelliJ Idea.

• Alt + 1 - Show/Hide Project Explorer
• Double Shift - Search Anything in IntelliJ Idea
• Increase Fonts - Double Shift and Search 'Increase Fonts'
• Decrease Fonts - Double Shift and Search 'Decrease Fonts'
• Ctrl + E - Navigate between files opened in Explorer
• Ctrl + Shift + E - Shows the last changed files
• Ctrl + Shift + N - Search all files
• Ctrl + N - Search only class files
• Ctrl + Alt + L - Reformat Code
• Ctrl + B - Open Declaration

I hope these shortcuts will also help you to improve your productivity. For complete list of shortcuts, please refer to the Jetbrains official website -

(https://www.jetbrains.com/help/idea/mastering-keyboard-shortcuts.html)