When you check ArrayList documentation, it says what are all the methods are inherited from which classes / interfaces.
There might be some of AbstractClasses which implement interface methods and those AbstractClasses will again be inherited by Concrete SubClasses.
ArrayList will inherit some AbstractClasses and hence the said methods are not implemeted in ArrayList.
Where as in LinkedList inherits some other Classes which might not implement the List classes.
Only ground rule is thta, the methods available in Interface should be implemnted by it's Classes which inherits it, if not, it will become AbstractClass.