LinkedList in Java

Linked lists are among the simplest and most common data structures . Arrays and Linked lists are similar since they both store collections of data. An array allocates memory for all its elements lumped together as one block of memory. In contrast, a linked list allocates space for each element separately in its own block of memory called a Node. The main disadvantage of using arrays to store data is that arrays are static structures and therefore cannot be easily extended or reduced to fit the data set. One disadvantage of a linked list over an array is that it does not allow direct access to the individual elements. If you want to access a particular item then you have to start at the head and follow the link until you get to that item.
How to Java LinkedList
Linked list is a data structure consisting of a group of nodes which together represent a sequence. It is dynamic in nature which allocates the memory when required. That means, the number of nodes in a list is not fixed and can grow and shrink on demand. Any application which has to deal with an unknown number of objects is a must to use a linked list. Each node in a Linked list contains two fields: a "data" field to store whatever element type the list holds for its client, and a "next" field which is a pointer used to link one node to the next node. The last node in the list has its .next field set to NULL to signify the end of the list.

There are three types of linked-list. They are:

  1. Single Linked List
  2. Doubly Linked List
  3. Circular Linked List
Single LinkedList : Single linked lists contain nodes which have a data part as well as an link part i.e. next, which points to the next node in sequence of nodes. Item navigation in Single linked lists are forward only. The operations we can perform on Single linked lists are insertion, deletion and traversal. Doubly LinkedList : In a doubly linked list, each node contains two links the first link points to the previous node and the next link points to the next node in the sequence. Unlike single linked-list, items can be navigated forward and backward in a doubly linked list. Circular LinkedList : In a circular linked list Last item contains link of the first element as next and the first element has a link to the last element as previous.

The following Java program illustrates several of the methods supported by this LinkedList collection Framework

import java.util.*; class TestClass { public static void main (String[] args) throws java.lang.Exception { //create a new linked list object LinkedList days = new LinkedList(); // add elements to the linked list days.add("Monday"); days.add("Tuesday"); days.add("Wednesday"); days.add("Thursday"); days.addLast("Friday"); //Display all the contents of the LinkedList Iterator<String> itr=days.iterator(); while(itr.hasNext()){ System.out.println(; } /*Add First and Last Element in linked list*/ days.addFirst("Sunday"); days.addLast("Saturday"); System.out.println("After Addition: " + days); //Insert an element in linked list days.add(0, "Days in a Week"); //add start of linked list days.add(4,"Middle"); //add in the middle of linked list days.add(9, "End"); //add in the lst of linked list System.out.println("After Insertion: " + days); //remove days.removeFirst(); days.remove(3); //remove forth element from list days.removeLast(); System.out.println("After Addition: " + days); //Remove an element from linked list days.remove("Monday"); //remove monday from list //System.out.println("Contents : " + days); // Number of items in the linked list int elements = days.size(); System.out.println("No. of elements linked list: " + elements); // Finding elements in the linked list boolean check = days.contains("Sunday"); if(check) System.out.println("Item found !!"); else System.out.println("Not in the list!! "); // update linked list or get and set a value in a linked list Object item = days.get(0); days.set(0, (String) item + "-First Day"); System.out.println("After modification : " + days); } }