how to draw circular doubly linked list?

Java Programming: Doubly Linked List?

• I need to fill in the Delete, Retrieve and Empty methods. 1) Delete method - takes no parameter, it removes the top double from the stack. If the stack is empty, it throws the exception EmptyException 2) Retrieve method - takes no parameter, it returns a double. This should be the double on the top of the stack. If the stack is empty, it throws the exception EmptyException 3) Empty - takes no parameters, it returns true if the stack is empty, it returns false if it is not empty public class DStack { public static class EmptyException extends Exception { private static final long serialVersionUID=0; }; public DStack() { // Set up the dummy node. Head = new node(); Head.Next = Head; Head.Previous = Head; }; // Put an item onto the stack public void Store(double Item) { // Store on the top of the stack, that is // insert it at the front of the doubly linked list. node afterMe = Head; node newNode = new node(); newNode.Item = Item; newNode.Previous = afterMe; newNode.Next = afterMe.Next; newNode.Previous.Next = newNode; newNode.Next.Previous = newNode; }; // Retreive a copy of the top item on the stack // Throws EmptyException if the stack is empty public double Retrieve() throws EmptyException { // The next line is fake, delete it. // You implement the real thing return Head.Item; }; // Delete the item on the top of stack // Throws EmptyException if the stack is empty public void Delete() throws EmptyException { // Delete the top element in the stack. // You implement the real thing }; // Return true if empty // return false if not empty public boolean Empty() { // You implement the real thing return false; }; // Print the contents of the stack. public void SummarizeForward() { // go to the first node in the list node Cur = Head.Next; // Cycle until we come back to the dummy node while (Cur != Head) { System.out.print(Cur.Item + " " ); Cur = Cur.Next; }; System.out.println(""); }; public void SummarizeBackward() { // go to the dummy node node Cur = Head; // go to the last node in the list Cur = Head.Previous; // Cycle until we come back to the dummy node while (Cur != Head) { System.out.print(Cur.Item + " " ); Cur = Cur.Previous; }; System.out.println(""); }; // The node record // Can't be static if we are going to genericize it. private class node { double Item; node Next; node Previous; }; // The head of the doubly linked list, // for the stack this points to the // dummy node. private node Head; };

• Answer:

  public void Delete() throws EmptyException { if(Empty() == true) throw new EmptyException(); Head = Head.Next; if(Head != null) Head.Previous = null; }; public double Retrieve() throws EmptyException { if(Empty() == true) throw new EmptyException() Node Temp = Head; Head = Head.Next if(Head != null) Head.Previous = null; return(Temp.Item); }; public boolean Empty() { return(Head == null); // AKA. True if it is empty, false otherwise };