Doubly Linked List - Java

import java.util.*;

class Nodes
{

  int data;
  Nodes llink,rlink;
}

 class Dlink
 {
   Nodes first=null;
   Nodes last=null;
   int nd=0;
   Scanner s=new Scanner(System.in);

    void add()
    {

     Nodes node=new Nodes();
     node.llink=null;
     node.rlink=null;
     System.out.println("Enter data");
     node.data=s.nextInt();

     if(first==null) first=last=node;

      else { last.rlink=node;node.llink=last; last=node;}

    nd++;
    }

    void disp()
    {
      Nodes t=new Nodes();
      System.out.println("1.Left to right or 2.right to left...");
      int op=s.nextInt();
      if(op==1)
      {
      t=first; 
      while(t!=null)
      {
       System.out.print(t.data + "<--->" );
       t=t.rlink;
       }
      
      }
      
      else
      {
        t=last;
        while(t!=null)
       {
       System.out.print(t.data + "<--->" );
       t=t.llink;
       }
            
      }
      System.out.println("NULL\n");     
      }

      void search()
      {

       System.out.println("Enter data...");
       int d=s.nextInt();
       Nodes t=first;int p=1;boolean found=false;
       while(t!=null)
       {

        if(t.data==d) {found=true;break;}
              t=t.rlink;
        p++;

        } 

        if(found) System.out.println("Found at pos ..."+ p ); 
        else System.out.println("Not found");
                   
       }

      void del()
      {

       System.out.println("Enter the pos........");
       int p=s.nextInt();
       if(p>nd) System.out.println("Invalid position");
       else
       {
       if(p==1) { first=first.rlink;
                 if(first==null) last=null; else first.llink=null;nd--;}
       else
       if(p==nd) { last=last.llink;
                  if(last==null) first=null;
                  else last.rlink=null;nd--;}
       else
        {
        Nodes t=first;int i=2; 
        while(i<p)  {t=t.rlink;i++;}
        Nodes tmp=t.rlink.rlink;
        t.rlink=tmp;
        tmp.llink=t;
        nd--;  

        }
      
       }
       }
     
}   

class Main
 {
   
   
 public static void main(String args[])
  {
   Scanner s=new Scanner(System.in);
   int op;
   Dlink dl=new Dlink();
   while(true)
   {

    System.out.println("1.add\n2.disp\n3.search\n4.del\n5.exit\n Enter Option");
    op=s.nextInt();

    switch(op)
    {
     case 1: dl.add();
             break;

    case 2: dl.disp();
            break;
    case 3: dl.search();
            break; 
    
    case 4: dl.del();
            break; 
    case 5:System.exit(0);  

     }

   }

   }

}

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