.isDisplayed - Selenium + Appium

I'm just a beginner in automation testing. Know only c, c++ and php. Now i want to learn java by working with automation tests.

I want to check if the element exist and if its visible, i found explaination on this page and for check if its visible i have to use .isDisplayed() method but i cant understand why my IDE cant find this method? when i call it, its "red" so not found.

There is a link to img from my ide: http://ift.tt/2eLKRUr

You can see that method .isEmpty() is normally working... but have no idea why .isDisplayes is red ;/

Couldnt upload this image cos my chrome doing some crazy shit when i'm uploading it.

Sorry for stupid question -> i'm learning