DSA using Java - Circular Linked List

Circular Linked List is a variation of Linked list in which first element points to last element and last element points to first element. Both Singly Linked List and Doubly Linked List can be made into as circular linked list
As per above shown illustrations, following are the important points to be considered.
Last Link'next points to first link of the list in both cases of singly as well as doubly linked list.
Last Link'next points to first link of the list in both cases of singly as well as doubly linked list.
First Link's prev points to the last of the list in case of doubly linked list.
First Link's prev points to the last of the list in case of doubly linked list.
Following are the important operations supported by a circular list.
insert − insert an element in the start of the list.
insert − insert an element in the start of the list.
delete − insert an element from the start of the list.
delete − insert an element from the start of the list.
display − display the list.
display − display the list.
Following code demonstrate insertion operation at in a circular linked list based on single linked list.
//insert link at the first location
public void insertFirst(int key, int data){
   //create a link
   Link link = new Link(key,data);
   if (isEmpty()) {
      first  = link;
      first.next = first;
   }      
   else{
      //point it to old first node
      link.next = first;
      //point first to new first node
      first = link;
   }      
}
Following code demonstrate deletion operation at in a circular linked list based on single linked list.
//delete link at the first location
public Link deleteFirst(){
   //save reference to first link
   Link tempLink = first;
   //if only one link
   if(first.next == null){
      last = null;
   }else {
      first.next.prev = null;
   }
   first = first.next;
   //return the deleted link
   return tempLink;
}
Following code demonstrate display list operation in a circular linked list.
public void display(){  
   //start from the beginning
   Link current = first;
   //navigate till the end of the list
   System.out.print("[ ");
   if(first != null){
      while(current.next != current){
         //print data
         current.display();
         //move to next item
         current = current.next;
         System.out.print(" ");
      }
   }
   System.out.print(" ]");
}
Link.java
package com.tutorialspoint.list;
   
public class CircularLinkedList {
   //this link always point to first Link 
   private Link first;

   // create an empty linked list 
   public CircularLinkedList(){
      first = null;       
   }

   public boolean isEmpty(){
      return first == null;
   }

   public int length(){
      int length = 0;

      //if list is empty
      if(first == null){
         return 0;
      }

      Link current = first.next;

      while(current != first){
         length++;
         current = current.next;   
      }
      return length;
   }

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

   //delete first item
   public Link deleteFirst(){
      //save reference to first link
      Link tempLink = first;
      if(first.next == first){  
         first = null;
         return tempLink;
      }     

      //mark next to first link as first 
      first = first.next;
      //return the deleted link
      return tempLink;
   }

   public void display(){

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

public class CircularLinkedListDemo {
   public static void main(String args[]){
      CircularLinkedList list = new CircularLinkedList();

      list.insertFirst(1, 10);
      list.insertFirst(2, 20);
      list.insertFirst(3, 30);
      list.insertFirst(4, 1);
      list.insertFirst(5, 40);
      list.insertFirst(6, 56);

      System.out.print("\nOriginal List: ");  
      list.display();
      System.out.println("");  
      while(!list.isEmpty()){            
         Link temp = list.deleteFirst();
         System.out.print("Deleted value:");  
         temp.display();
         System.out.println("");
      }         
      System.out.print("List after deleting all items: ");          
      list.display();
      System.out.println("");
   }
}
If we compile and run the above program then it would produce following result −
Original List: [ {6,56} {5,40} {4,1} {3,30} {2,20}  ]
Deleted value:{6,56}
Deleted value:{5,40}
Deleted value:{4,1}
Deleted value:{3,30}
Deleted value:{2,20}
Deleted value:{1,10}
List after deleting all items: [  ]

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