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  • Dequeue remove from the tail using node

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    hey there! whenever i run my program it works well but when im at removeTail() it crashes at last value,it works to delete from the back when im at the last value it crashes,any help? hope it makes sense.

    import java.util.Scanner;
    
    public class dequeue {
     public static void main(String[] args) {
    
      int choice = 1;
      Queuec Teller = new Queuec();
    
      while (choice != 99) {
       System.out.print("\n\t\t\t\tQueue Main Menu \n\n");
    
       System.out.println("\n\t\t\t\t1.Enqueue from the Head " + "\n\t\t\t\t2.Enqueue from the Tail "
         + "\n\t\t\t\t3.Dequeue from the Head" + "\n\t\t\t\t4.Dequeue from the Tail "
         + "\n\t\t\t\t5.The Top Element" + "\n\t\t\t\t99. Main Menu");
       System.out.println("\n\t\t\t\tEnter Your Choice:");
       Scanner mydata = new Scanner(System.in);
       choice = mydata.nextInt();
    
       switch (choice) {
       case 1:
        Teller.insertHead();
        System.out.println("\n-------------------------------------------------\n");
        break;
       case 2:
        Teller.insertTail();
        System.out.println("\n-------------------------------------------------\n");
        break;
       case 3:
        Teller.removeHead();
        System.out.println("\n-------------------------------------------------\n");
        break;
       case 4:
        Teller.removeTail();
        System.out.println("\n-------------------------------------------------\n");
        break;
       case 5:
        Teller.top();
        System.out.println("\n-------------------------------------------------\n");
        break;
       default:
        break;
       }
      }
     }
    }
    
    class Node {
    
     int data;
     Node next;
     Node prev;
    
     Node(int d) {
      data = d;
      next = null;
     }
    }
    
    class Queuec {
    
     Node head = null;
     Node prev;
     Node tail = null;
    
     public void insertHead() {
      System.out.println("\nEnter A Number To Insert At The Beginning: ");
      Scanner InputR = new Scanner(System.in);
      int R = InputR.nextInt();
    
      Node newhead = new Node(R);
      newhead.next = head;
      head = newhead;
    
      System.out.println("\n");
      System.out.println("The DeQueue:");
      Node j = head;
      while (j != null) {
       System.out.print(j.data + " ");
       j = j.next;
      }
      System.out.println("\n");
    
     }
    
     public void insertTail() {
      System.out.print("\nInsert At The End:");
      System.out.println("Enter Node value = ");
      Scanner FirstInput = new Scanner(System.in);
      int t = FirstInput.nextInt();
    
      Node newtail = new Node(t);
      newtail.next = null;
      Node tail = head;
      while (tail.next != null) {
       tail = tail.next;
      }
      tail.next = newtail;
      System.out.println("The List::");
      Node q = head;
      while (q != null) {
       System.out.print(q.data + " ");
       q = q.next;
      }
      System.out.println("\n");
     }
    
     public void removeHead() {
      Node j = head;
      if (j != null) {
       head = head.next;
       System.out.println("\n");
       System.out.println("The DeQueue:");
       while (j != null) {
        System.out.print(j.data + " ");
        j = j.next;
       }
       System.out.println("\n");
      } else {
       System.out.println("\nQueue is Empty!");
      }
     }
    
     public void removeTail() {
       if(head == null)
       {
         System.out.print("DeQueue is Empty!");
         return;
       }
    
       Node de = head;
    
       while (de.next.next != null){
         de = de.next;
       }
    
       de.next = null;
       System.out.println("\n");
       System.out.println("The DeQueue:");
       de = head;
       while (de != null) {
           System.out.print(de.data + " ");
           de = de.next;
       }
       System.out.println("\n");
     }
    
     public void top() {
      Node fimx = head;
      int max = head.data;
      while (fimx != null) {
       if (max < fimx.data) {
        max = fimx.data;
       }
    
       fimx = fimx.next;
      }
      System.out.println("\n");
      System.out.println("Top Value Stored In the DeQueue is:");
      System.out.println("Top = " + max);
      System.out.println("\n");
    
     }
    }


     

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