Double clicking works fine on Mac. Not sure about Linux.

There is mark occurrences features for java (please verify you settings in "Tools | Options | Editor " -> Mark occurrences) - selecting fields, variables ... should highlight all occurrences that exist in file (anyway, you should be able to navigate among them fast by ALT+UP (DOWN))

For general text selection, you can select desired piece of word and invoke "CTRL+F", entering the text there should highlight the occurences.

ok it took a long while before highlighting started to work for me, not sure why?

however i do notice an annoying behavior with highlight feature. In a rails project if I click on a function definition, like:

  def  self.find_by_password_and_email( _password, _email )
    #... some code
  end

the IDE will highlight something inside the function block and not the (referenced) function names used throughout the current file. if I click on the function name from a code referencing it, all the function names in current file get highlighted correctly.