Intellij IDEA show javadoc automatically

Settings | Editor | General |Code Completion | Autopopup documentation in (ms).

UPDATE: latest versions have an option to show JavaDoc on mouse move.

File -> Settings -> Editor -> Code completion.

Check Autopopup documentation in (ms) and choose delay.

Show Javadoc in IntelliJ IDEA 14:

• When you write code:

  File -> Settings -> Editor -> General -> Code Completion -> Autopopup documentation in (ms)

It's only available when you press CTRL+SPACE It's more usable if you select the pin icon when it popups. The documentation window will be added to the tabs on the right. Later on I recommend to resize the window and to uncheck the Pinned property.

• On mouse hover:

  File -> Settings -> Editor -> General -> Show quick documentation on mouse move