Question

if you look at the LinkedList methods of Java, it does offer operations for Queue, Stack, Deque.

And I am aware that you can implement Queue, Stack or Deque with a LinkedList. If you look at C# implementation though, Queue and Stack uses arrays.

My Curiosity is, why they offer a push(T e) method for a linked list?

Why Queue and Stack are not separate classes, just like C#.

Below is the code for push and pop which is duhhh. But why?

public void push(Object obj)
{
    addFirst(obj);
}

public Object pop()
{
    return removeFirst();
}

If you look at HashMap, or HashSet, it uses array internally, and there is LinkedHashSet and map correspondingly to keep ordering.

This is not really confusing, but it doesnt make sense really.

Why java has such implementation?

Answer 1

Focus on data structure implementation:

Linked list is efficient for frequent add and remove. (as Queue and Stack usually do, and iteration operation is rare). Array is not, it needs array-copy operation which is time consuming.