Linked List

Linked List Basics

Linked List is a sequence of links which contains items. Each link contains a connection to another link. Linked list the second most used data structure after array. Following are important terms to understand the concepts of Linked List.

Link − Each Link of a linked list can store a data called an element.
Next − Each Link of a linked list contain a link to next link called Next.
LinkedList − A LinkedList contains the connection link to the first Link called First.

Linked List Representation

As per above shown illustration, following are the important points to be considered.

LinkedList contains an link element called first.
Each Link carries a data field(s) and a Link Field called next.
Each Link is linked with its next link using its next link.
Last Link carries a Link as null to mark the end of the list.

Learn Java in-depth with real-world projects through our Java certification course. Enroll and become a certified expert to boost your career.

Types of Linked List

Following are the various flavours of linked list.

Simple Linked List − Item Navigation is forward only.
Doubly Linked List − Items can be navigated forward and backward way.
Circular Linked List − Last item contains link of the first element as next and and first element has link to last element as prev.

Basic Operations

Following are the basic operations supported by a list.

Insertion − add an element at the beginning of the list.
Deletion − delete an element at the beginning of the list.
Display − displaying complete list.
Search − search an element using given key.
Delete − delete an element using given key.

Insertion Operation

Insertion is a three step process:

Create a new Link with provided data.
Point New Link to old First Link.
Point First Link to this New Link.

//insert link at the first location
public void insertFirst(int key, int data){
   //create a link
   Link link = new Link(key,data);
   //point it to old first node
   link.next = first;
   //point first to new first node
   first = link;
}

Deletion Operation

Deletion is a two step process:

Get the Link pointed by First Link as Temp Link.
Point First Link to Temp Link’s Next Link.

//delete first item
public Link deleteFirst(){
   //save reference to first link
   Link tempLink = first;
   //mark next to first link as first 
   first = first.next;
   //return the deleted link
   return tempLink;
}

Navigation Operation

Navigation is a recursive step process and is basis of many operations like search, delete etc.:

Get the Link pointed by First Link as Current Link.
Check if Current Link is not null and display it.
Point Current Link to Next Link of Current Link and move to above step.

Note

//display the list
public void display(){
   //start from the beginning
   Link current = first;
   //navigate till the end of the list
   System.out.print("[ ");
   while(current != null){
  //print data
  current.display();
  //move to next item
  current = current.next;
  System.out.print(" ");   }
   System.out.print(" ]");
}

Advanced Operations

Following are the advanced operations specified for a list.

Sort − sorting a list based on a particular order.
Reverse − reversing a linked list.
Concatenate − concatenate two lists.

Sort Operation

We’ve used bubble sort to sort a list.

public void sort(){

   int i, j, k, tempKey, tempData ;
   Link current,next;
   int size = length();
   k = size ;
   for ( i = 0 ; i < size - 1 ; i++, k-- ) {
  current = first ;
  next = first.next ;
  for ( j = 1 ; j &lt; k ; j++ ) {            
     if ( current.data &gt; next.data ) {
        tempData = current.data ;
        current.data = next.data;
        next.data = tempData ;
        tempKey = current.key;
        current.key = next.key;
        next.key = tempKey;
     }
     current = current.next;
     next = next.next;                        
  }   }
}

Reverse Operation

Following code demonstrate reversing a single linked list.

public LinkedList reverse() { 
   LinkedList reversedlist = new LinkedList();
   Link nextLink = null;     
   reversedlist.insertFirst(first.key, first.data);

   Link currentLink = first;       
   // Until no more data in list, 
   // insert current link before first and move ahead.
   while(currentLink.next != null){
  nextLink = currentLink.next;           
  // Insert at start of new list.
  reversedlist.insertFirst(nextLink.key, nextLink.data); 
  //advance to next node
  currentLink = currentLink.next;               }      
   return reversedlist;
}

Concatenate Operation