In Java, please!

// TO DO: add implementation and JavaDocs.

import java.util.ArrayList;

import java.util.Iterator;

public class DLList implements Iterable {

// doubly linked list with both head and tail, no dummy nodes

private Node head; //beginning of list

private Node tail; //end of list

// ADD MORE PRIVATE MEMBERS HERE IF NEEDED!

//constructor

// initialize the list to being an empty list

public DLList() {

}

// report number of items

// O(1)

public int size() {

//default return, remove or updated as needed

return null;

}

// returns the first value from the beginning of the list

// do not remove the value!

// return null if list is empty

// O(1)

public T getFirst() {

//default return, remove or updated as needed

}

// inserts a new node with value at the begining of the list

// you can assume value is not null

// O(1)

public void addFirst(T value) {

}

// remove and return the first value in the list

//return null if list is empty

// O(1)

public T removeFirst(){

//default return, remove or updated as needed

return null;

}

// returns the last value from the end of the list

// do not remove the value!

// return null if list is empty

// O(1)

public T getLast() {

//default return, remove or updated as needed

return null;

}

// inserts a new value at the end of the list

// you can assume value is not null

// O(1)

public void addLast(T value) {

}

// remove and return the last value from the end of the list

//return null if list is empty

// O(1)

public T removeLast(){

//default return, remove or updated as needed

return null;

}

//remove and return the first occurence of value

// (i.e. the occurence that is closest to head)

// - return null if value is not present

// - note: must return the data from list, not the argument value

//O(n) where n is the number of items

public T remove(T value){

//default return, remove or updated as needed

return null;

}

// return a string representing the values in the list starting from index to end,

// seperated by a single space

// return empty string for invalid start or empty list

// O(n) where n is the number of items

// Warning: concatenating String objects will yield a O(n^2) solution

public String listToString(int start) {

//default return, remove or updated as needed

return null;

}

// return a string representing the values in the list, from end to beginning,

// seperated by a single space

// return empty string for an empty list

// O(n) where n is the number of items

// Warning: concatenating String objects will yield a O(n^2) solution

public String listToStringBackward() {

//default return, remove or updated as needed

return null;

}

public Iterator iterator() {

//Return an iterator that traverses from

//the beginning (head) to the end (tail) of the list

//The iterator's hasNext() and next() methods

//must both be O(1)

//next() should throw a NullPointerException

//if you try to use next when there are no

//more items (any error message is fine).

//update / replace this dummy return statement as needed

return null;

}

public Iterator backwardIterator() {

//Return an iterator that traverses from

//the end (tail) to the beginning (head) of the list

//The iterator's hasNext() and next() methods

//must both be O(1)

//next() should throw a NullPointerException

//if you try to use next when there are no

//more items (any error message is fine).

//update / replace this dummy return statement as needed

return null;

}