Doubly Linked List implementation

class Link {
public int iData; //data item
public Link next; //next link in the list
public Link previous; //previous link in the list

public Link(int id) {
iData = id;
}

//display the elements in the list

public void displayList(){
return "{" + iData + "} ";
}
}

/*another class which contains the methods for the program*/

class DoublyLinkedList {
private Link first;
private Link last;

public DoublyLinkedList() {
first = null;
last = null;
}

public boolean isEmpty() {
return first == null;
}

public void insertFirst(int dd) {
Link newLink = new Link(dd);
if (isEmpty()){
last = newLink;
}else{
first.previous = newLink;
}
newLink.next = first;
first = newLink;
}

public void insertLast(int dd) {
Link newLink = new Link(dd);
if (isEmpty()){
first = newLink;
}else {
last.next = newLink;
newLink.previous = last;
}
last = newLink;
}

public Link deleteFirst() {
Link temp = first;
if (first.next == null){
last = null;
}else{
first.next.previous = null;
}
first = first.next;
return temp;
}

public Link deleteLast() {
Link temp = last;
if (first.next == null){
first = null;
}else{
last.previous.next = null;
}
last = last.previous;
return temp;
}

public boolean insertAfter(int key, int dd) {
Link current = first;
while (current.iData != key) {
current = current.next;
if (current == null){
return false;
}
}
Link newLink = new Link(dd);

if (current == last) {
newLink.next = null;
last = newLink;
} else {
newLink.next = current.next;

current.next.previous = newLink;
}
newLink.previous = current;
current.next = newLink;
return true;
}

public Link deleteKey(int key) {
Link current = first;
while (current.iData != key) {
current = current.next;
if (current == null)
return null;
}
if (current == first){
first = current.next;
}else{
current.previous.next = current.next;
}

if (current == last){
last = current.previous;
}else{
current.next.previous = current.previous;
}
return current;
}

}

[TUTORIAL_DOUBLY]

http://dept-info.labri.u-bordeaux.fr/~strandh/Teaching/MTP/Common/Strandh-Tutorial/double-list.html

[WIKI]

http://en.wikipedia.org/wiki/Linked_list