Program Sederhana Membuat Aplikasi Double Linked List menggunakan Bahasa Java

Class Node 

public class Node{
    int data;
    Node next;
    Node prev;
    
    public Node(int data){
        this.data = data;
    }
    
    public void tampil(){
        System.out.print("("+data+")");
    }
}

Class DoublyLinkedList

public class DoubleLinkedList{
    Node first;
    Node last;
    
    public DoubleLinkedList(){
        first = null;
        last = null;
    }
    
    public boolean isEmpty(){
        return (first == null);
    }
    
    public void insertFirst(int data){
        Node node = new Node(data);
        if(isEmpty()){
            last = node;
        }
        else{
            first.prev = node;
        }
        node.next = first;
        first = node;
    }
    
    public void insertLast(int data){
        Node node = new Node(data);
        if(isEmpty())
            first = node;
        else{
            last.next = node;
            node.prev = last;
        }
        last = node;
    }
    
    public Node deleteFirst(){
        Node temp = first;
        if(first.next == null)
            last = null;
        else
            first.next.prev = null;
        first = first.next;
        return temp;
    }
    
    public Node deleteLast(){
        Node temp = last;
        if (first.next == null)
            first = null;
        else
            last.prev.next = null;
        last = last.prev;
        return temp;
    }
    
    public boolean insertAfter(int key, int data){
        Node current = first;
        while(current.data != key){
            current = current.next;
            if(current == null)
            return false;
        }
        Node node = new Node(data);
        
        if (current==last){
            node.next = null;
            last = node;
        }
        else{
            node.next = current.next;
            
            current.next.prev = node;
        }
        node.prev = current;
        current.next = node;
        return true;
    }
    
    public Node deleteKey(int key){
        Node current = first;
        while(current.data != key){
            current = current.next;
        if(current == null)
            return null;
        }
        if(current == first)
            first = current.next;
        else
            current.prev.next = current.prev;
            return current;
    }
    
    public void displayForward(){
        System.out.print("List | First -> Last : ");
        Node current = first;
        
        while(current != null){
            current.tampil();
            current = current.next;
        }
        System.out.println("");
    }
    
    public void displayBackward(){
        System.out.print("List | Last -> First : ");
        Node current = last;
        while(current != null){
            current.tampil();
            current = current.prev;
        }
        System.out.println("");
    }
}

Class APP

public class APP{
    public static void main(String[] args){
        DoubleLinkedList list = new DoubleLinkedList();
        list.insertFirst(10);
        list.insertFirst(15);
        list.insertFirst(20);
        list.insertLast(30);
        list.insertLast(35);
        list.insertLast(40);
        list.displayForward();
        list.displayBackward();
        list.deleteFirst();
        list.deleteLast();
        list.deleteKey(15);
        list.displayForward();
        list.insertAfter(10, 90);
        list.insertAfter(30, 95);
        list.displayForward();
    }
}

>>> Link Github <<<