Add and delete elements of doubly linked list

/** 
 * @author Eightn0 
 * @create 2021-03-13 20:36 
 * Doubly linked list: one field stores data, two fields store pointers, one pointer points to the next node, and the other pointer points to the previous node 
 * llink- data-rlink 
 * Insert: Insert at the first position: point the right link of the new node to the first node of the original table, and the left link to null 
 * Point the left link of the first node of the 
 original table to the new node * Change the original table The head pointer head points to the new node 
 * Insert at the last position: the right link of the last node of the original table points to the new node 
 * The left link of the new node points to the last node of the original table, and the right link points to null 
 * in the middle position Insert: remember that the left of the new node is ptr, which is again rtr 
 * ptr The right link points to the new node 
 * The left link of the new node points to ptr, the right link points to rtr 
 * rtr The left link points to the new node 
 * Delete: delete the first node: header Pointer head points to the next 
 * New table head pointer points to null 
 * Delete the last node: the right pointer of the penultimate node points to null 
 * Delete the middle node: the right link of the previous node points to the next
 * The left link of the next node points to the previous 
 */ 

class Node { 
    int data; 
    Node rnext; 
    Node lnext; 

    public Node(int data) { 
        this.data = data; 
        this.rnext = null; //Every node has Left pointer and right pointer, the default is null, and then assign 
        this.lnext = null; 
    } 
} 
public class Doubly { 
    private Node first; 
    private Node last; 

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

    public void print( ){ 
        Node current = first; 
        while (current != null){ 
            System.out.println("["+current.data+"]"); 
            current = current.rnext;
        } 
        System.out.println(); 
                    last.rnext = newN;//The end of the table The right link points to the new node 
    }

    /*Insert node*/ 
    public void insert(Node newN){ 
        Node tmp; 
        Node newNode; 
        if (isEmpty()){ 
            first = newN; 
            first.rnext = last; 
            last = newN; 
            last.lnext = first; 
        }else { 
            if (newN.lnext == null){//Insert the header 
                first.lnext = newN;//The left link of the original header points to the new node 
                newN.rnext = first;//The right pointer of the new node points to the original header 
                first = newN ;//The head of the table moves to the new pointer, the order can not be disordered 
            }else { 
                if (newN.rnext == null){//Insert the end of the table 
                    last = newN ; //The end of the new table points to the new node
                    newN.lnext = last;//The left link of the new node points to the end of the original table 
        Node newNode;
                }else {//Insert the middle 
                    newNode = first; 
                    tmp = first; 
                    while (newN.rnext != newNode.rnext){ 
                        tmp = newNode; 
                        newNode = newNode.rnext;//Search process 
                    } 
                    tmp.rnext = newN;// Insertion process 
                    newN.rnext = newNode; 
                    newNode.lnext = newN; 
                    newN.lnext = tmp; 
                } 
            } 
        } 
    } 

    /*Delete node*/ 
    public void delete(Node delNode){ 
        if (first == null){/ / Determine whether the linked list is empty
        Node tmp; 
            System.out.println("[The table is empty]"); 
            return; 
        } 
        if (delNode == null){//Determine whether the delete condition exists 
            System.out.println("[Error: del is not a table Node]"); 
            return; 
        } 
        if (first.data == delNode.data){//Delete the header 
            first = first.rnext;//Start moving to the second node 
            first.lnext = null;// Set the left link of the second node to null 
        }else if (last.data == delNode.data){//Delete the end of the table 
            newNode = first; 
            while (newNode.rnext != last) newNode = newNode.rnext; 
            newNode .rnext = null; 
            last = newNode; 
        }else {//Delete the node in the middle of the table 
            newNode = first;
            tmp = first;
            while (newNode.data != delNode.data){ 
                tmp = newNode;//Search process 
                newNode = newNode.rnext; 
            } 
            tmp.rnext = delNode.rnext;//Delete process 
            tmp.lnext = delNode.lnext; 
        } 
    } 
}