$//===============================================$ Requirements

$//$

$//$ Please complete MyDoublyLinkedList class.

$//$

$//$ The output should be:

$//$

$//$ Test MyDoublyLinkedList:.....

$//(1,2,3,4,5)$

$//(-2,-1,1,2,3,4,5)$

$//(-2,100,-1,1,2,3,4,5)$

$//(100,-1,1,2,3,4,5)$

$//(100,-1,1,2,3,4)$

$//$

$//===============================================$ Note

$//$

$//1.$ DO NOT DELETE ANY COMMENT!!!

$//2.$ Modify the file name to "MyDoublyLinkedList.java" before compiling it$.$

$//$

$//===============================================$

public class MyDoublyLinkedList $\{$

$//---------------------$ Data field

public Node header; $//$ parent of head, dummy node

public Node trailer; $//$ child of tail, dummy node

public int size $=0$;

$//---------------------$ Method field

public MyDoublyLinkedList$()\{$

header $=$ new Node$<>($null$,$ null, null$)$;

trailer $=$ new Node$<>($null$,$ header, null$)$; $//$ header $<--$ trailer

header.setNext$($trailer$)$; $//$ header $-->$ trailer

$\}$

public int size$()\{$ return size; $\}$

public boolean isEmpty$()\{$ return size $==0$; $\}$

public E first$()\{$

if $($isEmpty$())$ return null;

return header.getNext$().$getElement$()$;

$\}$

public E last$()\{$

if $($isEmpty$())$ return null;

return trailer.getPrev$().$getElement$()$;

$\}$

public void addFirst$($E e$)\{$

addBetween$($e$,$ header, header.getNext$())$;

$\}$

public void addLast$($E e$)\{$

addBetween$($e$,$ trailer.getPrev$(),$ trailer$)$;

$\}$

public E removeFirst$()\{$

if $($isEmpty$())$ return null;

return remove$($header$.$getNext$())$;

$\}$

public E removeLast$()\{$

if $($isEmpty$())$ return null;

return remove$($trailer$.$getPrev$())$;

$\}$

private void addBetween$($E e$,$ Node predecessor, Node successor$)\{$

$//$ Complete this block

$\}$

private E remove$($Node node$)\{$

$//$ Complete this block

$\}$

public String toString$()\{$

StringBuilder sb $=$ new StringBuilder$("(")$;

Node walk $=$ header.getNext$()$;

while $($walk $!=$ trailer$)\{$

sb$.$append$($walk$.$getElement$())$;

walk $=$ walk.getNext$()$;

if $($walk $!=$ trailer$)$

sb$.$append$(",")$;

$\}$

sb$.$append$(")")$;

return sb$.$toString$()$;

$\}$

public static void main$($String$[]$ args$)\{$

System.out.println$("$Test MyDoublyLinkedList:....."$)$;

MyDoublyLinkedList list $=$ new MyDoublyLinkedList$()$;

list.addLast$(1)$;

list.addLast$(2)$;

list.addLast$(3)$;

list.addLast$(4)$;

list.addLast$(5)$;

System.out.println$($list$.$toString$())$; $//(1,2,3,4,5)$

list.addFirst$(-1)$;

list.addFirst$(-2)$;

System.out.println$($list$.$toString$())$; $//(-2,-1,1,2,3,4,5)$

list.addBetween$(100,$ list.header.getNext$(),$ list.header.getNext$().$getNext$())$;

System.out.println$($list$.$toString$())$;

list.removeFirst$()$;

System.out.println$($list$.$toString$())$;

list.removeLast$()$;

System.out.println$($list$.$toString$())$;

$\}$

$\}$

$//-----------$ Node class $-----------$

class Node $\{$

private E element;

private Node prev;

private Node next;

public Node$($E e$,$ Node p$,$ Node n$)\{$

element $=$ e;

prev $=$ p;

next $=$ n;

$\}$

public E getElement$()\{$ return element; $\}$

public Node getPrev$()\{$ return prev; $\}$

public Node getNext$()\{$ return next; $\}$

public void setPrev$($Node p$)\{$ prev $=$ p; $\}$

public void setNext$($Node n$)\{$ next $=$ n; $\}$

$\}$

$//-----------$ end of Node class $-----------$