The Edit | Copy Reference action can be used to insert a reference to a field/method/class/file into the current position in the editor.
For example, go to the java.util.Collections JDK class, position to the text cursor at the EMPTY-MAP field and press &shortcut:CopyReference;:

Then return to your Java source and press &shortcut:$Paste;:

You can also copy references in GotoClass/GotoSymbol/GotoFile dialogs.
Just press &shortcut:$Copy; on any element in the lookup list.