why LinkedList doesn't have initialCapacity in java?

Question

I wonder why LinkedList doesn't have initialCapacity .

I know good when to use ArrayList and when LinkedList .

Its good practice to define Collection final size like:

List<String> arraylist = new ArrayList<String>(5);

For LinkedList for example:

List<String> linkedlist = new LinkedList<String>(); // right way

but

List<String> arraylist = new LinkedList<String>(5); // compilation error

Can somebody spread a light on that issue?

[EDIT]

BTW, I can write

List<String> arraylist = new ArrayList<String>(5);
List<String> linkedlist = new LinkedList<String>(arraylist);

Answer 1

LinkedList by nature does not have "capacity", since it does not allocate memory to the items before the items are added to the list. Each item in a LinkedList holds a pointer to the next in the list.

There would be no point in allocating memory to the list beforehand, since LinkedList does not have capacity .

Answer 2

Its model is not based on an array but rather a true linked list, and so there is no need and further it would not make sense. It doesn't make much sense to have empty links like you have empty array items.

Answer 3

Why would you need a capacity on a LinkedList? A LinkedList does not work with fixed sized arrays. Every LinkedListElement has a pointer (a link!) to the next Element in the list. Which Because of that it is possible to add an element to a linked list in constant time. But it is costly to have random access to the elements in the List. You need to go through all the Elements in the list until you reach your destination.

Answer 4

Why would LinkedList have an initial capacity?

ArrayList is backed up by an array, so the initial capacity is the initial size of the array. LinkedList has no need of that.

Answer 5

Linkedlist does not need an initial value. Thats is the primary difference between array and linked list.

array will end somewhere. But linkedlist not. Linked list does not work on boundary values.

Answer 6

When you declare an array you have to know its size because pointers need to be created in memory. A linked list does not need this because there is no need for pointers to memory before any object is added to the list.

A linked list is defined recursively as: an empty list en element that points to the empty list

therefore whenever you add an element, you allocate memory (or rather in Java the compiler does this) when you create the element, and then when you add it to the list it now points to the list (or the last element in the list points to it).

So you don't need to declare initial size of linked list because a linked list always starts with the empty list, and when an element is added it points to the list.

Answer 7

ArrayList has an underlying array which needs to have a predefined limit and which is constantly updated . LinkedList, on the other hand, simply grows/shrinks since there is no underlying data structure.

Answer 8

ArrayList And LinkedList both have implementation class of List Interface.

ArrayList is using Resizable Array or Grow-able Array.In array Data structure using Contiguous memory allocation and with the help of that we can access array's element with index. When we declare any array then we should declare initial capacity because finding of Contiguous memory blocks for storing array's element.

LinkedList is using double linked list as under Line data structure. In linked list data structure using non contiguous memory allocation and using head and tail concept for access these element. So in LinkedList we don't need to any initial capacity.