Queue Implementation

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

public String toString() {
return "{" + iData + "} ";
}
}

class LinkList {
private Link first;

public LinkList() {
first = null;
}

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

public void insertFirst(int dd) {
Link newLink = new Link(dd);
newLink.next = first;
first = newLink;
}

public int deleteFirst() {
Link temp = first;
first = first.next;
return temp.iData;
}

public String toString() {
String str = "";
Link current = first;
while (current != null) {
str += current.toString();
current = current.next;
}
return str;
}
}

class FirstLastList {
private Link first;

private Link last;

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

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

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

public void insertLast(int dd) {
Link newLink = new Link(dd);

if (isEmpty())
first = newLink;
else
last.next = newLink;
last = newLink;
}

public int deleteFirst() {
int temp = first.iData;
if (first.next == null)
last = null;
first = first.next;
return temp;
}

public String toString() {
String str = "";
Link current = first;
while (current != null) {
str += current.toString();
current = current.next;
}
return str;
}
}

class LinkQueue {
private FirstLastList theList;

public LinkQueue() {
theList = new FirstLastList();
}

public boolean isEmpty() {
return theList.isEmpty();
}

public void insert(int j) {
theList.insertLast(j);
}

public double remove() {
return theList.deleteFirst();
}

public String toString() {
return theList.toString();
}
}

public class MainClass {
public static void main(String[] args) {
LinkQueue theQueue = new LinkQueue();
theQueue.insert(20);
theQueue.insert(40);
System.out.println(theQueue);

theQueue.insert(60);
theQueue.insert(80);

System.out.println(theQueue);

theQueue.remove();
theQueue.remove();

System.out.println(theQueue);
}
}


Reference:http:www.java2s.com/Tutorial/Java/0140_Collections/AQueueImplementedbyaLinkedList.html