Regarding the heading of your question:

get first and last element in ArrayList in Java

It should be pretty simple:

mimeList.get(0); // To get first
mimeList.get(mimeList.size()-1); //to get last

And regarding your if condition :

if(!(i==0 || i==mimeList.size()-1))

As you phrased it like:

if the element in mimeList is first or last it will go in else condition other wise in if condition

I used ! in if condition. Otherwise below is pretty cool:

if((i>0) && (i!=mimeList.size()-1))

One way is to use a Stream and map each of the inner arrays to its first element:

List<String> firstElements = yourList.stream()
                                     .map(x -> x[0].toString()) // you might need toString() here if your array is an Object[]
                                     .collect(Collectors.toList());

If you would like an array of strings instead:

String[] firstElements = yourList.stream()
                                     .map(x -> x[0].toString()) // you might need toString() here if your array is an Object[]
                                     .toArray(String[]::new);

I also suggest you to not use nested arrays like this. You should create a class with the properties you want to store and create a List of your class.

See the javadoc

of List

list.get(0);

or Set

set.iterator().next();

and check the size before using the above methods by invoking isEmpty()

!list_or_set.isEmpty()