LinkedList in Java with Examples

In the previous post, we learned how to make our own custom Linked list, and in this post, we will be learning about the inbuilt linked list class in Java, which is a part of the Java Collection framework. This Linked list class is present in java.util package.

First, let’s learn about what is a linked list –

• A linked list is a linear data structure that is used to store elements at non-contiguous memory locations
• A linked list is made up of nodes and each node is made up of two things
  • Data
  • Address
• Data contains the actual value that is to be stored in the linked list
• And the Address will contain the address of the next node or the previous node, depending on whether it is a singly linked list or a doubly linked list

There are three types of linked lists in general that we would like to point out here –

• Singly-linked list – A node only has a reference to the next node in a singly linked list. So, we can only move in one direction in a singly linked list.

• Doubly linked list – A node references both the previous and the subsequent node in a doubly linked list, except the head node or the first node, which only has a reference to the next node in the linked list. So, we can move in both directions in a doubly linked list.

• Circular linked list – A circular linked list is a singly linked list, with the difference that the last node points back to the first(head) node.

The inbuilt linked list class is a doubly-linked list, which means it can move in either direction to perform various operations. There are other features of Linked List in java –

• It maintains the insertion order.
• It is non-synchronized.

Declaration of Linked List class

public class LinkedList<E>
    extends AbstractSequentialList<E>
    implements List<E>, Deque<E>, Cloneable, java.io.Serializable

Now, here you can see that it extends the AbstractSequentialList class and implements the List, Deque interfaces. As List and Deque internally extends the Collection interface, the Linked List class also has to override the unimplemented methods of the Collection interface.

How to make Linked List Objects or call its constructors

There are two ways of creating a Linked list class object, one is by using the default constructor, and another one is by using the parameterized constructor.

The default constructor of the Linked List class –

It will create an empty linked list.

    /**
     * Constructs an empty list.
     */
    public LinkedList() {

    }

The parameterized constructor of the Linked List class –

It will take the collection as the argument.

    /**
     * Constructs a list containing the elements of the specified
     * collection, in the order they are returned by the collection's
     * iterator.
     *
     * @param  c the collection whose elements are to be placed into this list
     * @throws NullPointerException if the specified collection is null
     */
    public LinkedList(Collection<? extends E> c) {
        this();
        addAll(c);
    }

Now to make a linked list, we can use the default constructor as shown below –

LinkedList<String> linkedList = new LinkedList<String>();

Here, <String> is telling the linked list class that it will contain elements of type String. Here we can use any class, but don’t try to use primitive like int, float, double, etc., as it will throw you an error 😛

Linked list class methods

There are many helper methods in Linked last to facilitate various things. Some of them are listed below –

codekru.com/…/linked-list-contains-and-containsall-method

Hope you have liked the article. If you have any doubts or concerns, please feel free to write us in the comments or mail us at admin@codekru.com.

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