Circular doubly linked list and implementation

 

class Node<E>{
    E item;
    Node prev, next;
    
    Node(E newItem){
        item = newItem;
        prev = next =null;
    }
}

class CircularDoublyLinkedList{
    private Node head;
    private Node tail;
    private int size;
    
    CircularDoublyLinkedList(){
    
    }
    
    void addFirst(Node n){
        if(size == 0) head = tail = n;
        else if(size == 1){
            head = n;
            head.next = tail;
            head.prev = tail;
            tail.prev = head;
            tail.next = head;
        }
        else{
            head.prev = n;
            n.next = head;
            n.prev = tail;
            head = n;
            tail.next = head;
        }
        size ++;
    }
    
    void addLast(Node n){
        if(size == 0) head = tail = n;
        else if(size == 1){
            head.next = n;
            head.prev = n;
            n.prev = head;
            n.next = head;
            tail = n;
        }
        else {
            tail.next = n;
            n.prev = tail;
            n.next = head;
            head.prev = n;
            tail = n;
        }
        size ++;
    }
    
    void add(int index, Node n){
        if(index == 0) addFirst(n);
        else if(index >= size) addLast(n);
        else{
            Node cur = head;
            for(int i = 1; i < index; i++)
                cur = cur.next;
            Node temp = cur.next;
            cur.next = n;
            n.prev = cur;
            n.next = temp;
            temp.prev = n;
            size ++;
        }
    }
    
    Node removeFirst(){
        Node remove = head;
        if(size == 0) return null;
        else if(size == 1)
            head = tail =null;
        else if(size == 2){
            head = tail;
            head.prev = null;
            head.next = null;
        }
        else{
            Node temp = head.next;
            temp.prev = tail;
            tail.next = temp;
            head = temp;
        }    
        size --;
        return remove;
    }
    
    Node removeLast(){
        Node remove = tail;
        if(size == 0) return null;
        else if(size == 1)
            head = tail = null;
        else if(size == 2){
            tail = head;
            head.prev = null;
            head.next = null;
        }
        else{
            Node temp = tail.prev;
            temp.next = head;
            head.prev = temp;
            tail = temp;
        }
        size --;
        return remove;
    }
    
    Node remove(int index){
        if(index < 0 || index >= size) return null;
        else if(index == 0) return removeFirst();
        else if(index == size - 1) return removeLast();
        else{
            Node previous = head;
            for(int i = 1; i < index; i ++)
                previous = previous.next;
            Node remove = previous.next;
            Node temp = remove.next;
            previous.next = temp;
            temp.prev = previous;
            size --;
            return remove;
        }
    }
}