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package rd222dv_assign2.Queues;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
The {@code LinkedQueue} class represents a first-in-first-out (FIFO)
* queue of generic items.
* It has the <em>enqueue</em> and <em>dequeue</em>
* methods, together with other methods, such as first and last, looking at the first and last Object, and
* testing if the queue is empty, iterating through the Objects in first in first out order
* and a toString method for a nice String output.
*
* The <em>enqueue</em>, <em>dequeue</em>, <em>first</em>, <em>last</em>, <em>size</em>, and <em>is-empty</em>
* operations all take constant time in the worst case.
* <ul>
* <li> {@link rd222dv_assign2.Queues.LinkedQueue} </li>
* </ul>
*
* @author Ruth Dirnfeld
* @version 1.0
* @since 2017-02-05
*/
public class LinkedQueue implements Queue {
// Fields
private int size = 0;
private Node head = null;
private Node tail = null;
/**
* This constructs an empty linked queue.
*/
public LinkedQueue() {
}
/**
* This is a inner Node class which helps to reference the element in the
* queue.
*/
private class Node {
// Fields
private Object data;
private Node next;
}
/**
* Return the size of queue
*/
@Override
public int size() {
return size;
}
/**
* Return true if queue is empty,Otherwise false.
*/
@Override
public boolean isEmpty() {
return head == null;
}
/**
* Insert Object at last position of the queue.
*
* @param element Object to be added
*
*
*/
@Override
public void enqueue(Object element) {
/*
* If queue is empty, insert the element at the beginning. That element
* will be the first and last element of the queue. If not, put the
* element next to the tail node and change the tail node position which
* represent this new element. Increase the size in both cases.
*/
if (isEmpty() == true) {
Node newNode = new Node();
newNode.data = element;
head = newNode;
tail = head;
} else {
Node newNode = new Node();
newNode.data = element;
tail.next = newNode;
tail = tail.next;
}
size++;
}
/**
* This method returns and removes the Object at position first in the
* queue.
*
* If the queue is empty, this methods throws NoSuchElementException.
*/
@Override
public Object dequeue() {
/*
* If empty, throw exception. Otherwise, remove and return the first
* element and change the head node next to this element. Decrease the
* size.
*/
if (isEmpty() == true) {
throw new NoSuchElementException();
}
Object element = head.data;
head = head.next;
size--;
return element;
}
/**
* This method returns the Object at position first in the queue.
*
* If the queue is empty, this methods throws NoSuchElementException.
*/
/*
* I tried to write the throws like
*
* @throws NoSuchElementException, but the console gives error. Then I
* searched online http://www.javapractices.com/topic/TopicAction.do?Id=171
* and I read that I must avoid throws in java doc because it generates it
* automatically. Please suggest me if this is not true.
*/
@Override
public Object first() {
/*
* If empty, throw exception. Otherwise, return the first element.
*/
if (head == null) {
throw new NoSuchElementException();
} else
return head.data;
}
/**
* This method returns the Object at position last in the queue.
*
* If the queue is empty, this methods throws NoSuchElementException.
*/
@Override
public Object last() {
/*
* If empty, throw exception. Otherwise, return the last element.
*/
if (tail == null) {
throw new NoSuchElementException();
} else
return tail.data;
}
/**
* Represent all the elements in the queue.
*
* @return String
*
*/
@Override
public String toString() {
/*
* Add all the element from head to tail in the string builder. If
* empty, return empty queue.
*
*/
StringBuilder str = new StringBuilder();
Node newNode = new Node();
newNode = head;
str.append("[");
while (newNode != null) {
str.append(" " + newNode.data);
newNode = newNode.next;
}
str.append(" ]");
return str.toString();
}
/**
* Runs over all the element present in the queue.
*
* @return Iterator
*/
@Override
public Iterator iterator() {
return new LinkedQueueIterator();
}
// Inner iterator class
private class LinkedQueueIterator implements Iterator {
// field
private Node position;
// constructor
public LinkedQueueIterator() {
position = null;
}
/**
* Return true until the iterator does reached up to last Object of the
* queue.
*
* @return boolean
*/
@Override
public boolean hasNext() {
/*
* In the beginning, position is null, so this method will return
* true only if queue is not empty, otherwise false. In other case,
* position is increasing by 1, this method will return true until
* position is not reached up to the tail.
*/
if (position == null) {
return head != null;
} else
return position.next != null;
}
/**
* This method return Object until the hasnNext() method is true.
*
* @return Object
*/
@Override
public Object next() {
/*
* Throw error if iterator already runs over all the elements in the
* queue. In the first case, this method will only run if above
* method is true. In the last case, it will return elements until
* the position will not reached up to the tail.
*/
if (!hasNext()) {
throw new NoSuchElementException();
}
if (position == null) { //
position = head;
} else {
position = position.next;
}
return position.data;
}
}
}
/*
public class LinkedQueue implements Queue {
private class Node {
public Object data;
public Node next;
public Node(Object data, Node next) {
this.data = data;
this.next = next;
}
}
private Node head = null;
private Node tail = null;
/**
* Constructs a LinkedQueue with no detail message.
* Elements can be enqueued and dequeued to the LinkedQueue.
*/
/* public LinkedQueue(){}
/**
* Returns the number of items in this queue.
* Returns the number of items in this queue
*/
/* @Override
public int size() { // current queue size
int count = 0;
for (Node node = head; node != null; node = node.next) {
count++;
}
return count;
}
/**
* Returns true if this queue is empty;
*
* @return true if this queue is empty; otherwise false
*/
/* @Override
public boolean isEmpty() { // true if queue is empty
return head == null;
}
/**
* Adds the element to this queue.
* adds element at end of queue
*/
/* @Override
public void enqueue(Object element) { // add element at end of queue
Node newNode = new Node(element, null);
if (isEmpty()) {
head = newNode;
} else {
tail.next = newNode;
}
tail = newNode;
}
/**
* Removes and returns the element from this queue that was recently added.
* @return the element from this queue that was recently added
* @throws java.util.NoSuchElementException if this queue is empty
*/
/* @Override
public Object dequeue() { // return and remove first element.
if (isEmpty()) {
throw new NoSuchElementException("Is Empty");
}
Object element = head.data;
if (tail == head) {
tail = null;
}
head = head.next;
return element;
}
/**
* Returns the Object recently added to this queue.
* @return the Object recently added to this queue
*/
/* @Override
public Object first() { // return (without removing) first element
if (head == null) {
throw new NoSuchElementException();
} else {
return head.data;
}
}
/**
* Returns (without removing) last element from this queue.
* @return (without removing) last element from this queue.
*/
/* @Override
public Object last() { // return (without removing) last element
if (tail == null) {
throw new NoSuchElementException();
} else {
return tail.data;
}
}
/**
* Returns an iterator that iterates over the Objects in first in first out order
* @return an iterator that iterates over the Objects in first in first out order
*/
/* @Override
public Iterator<Object> iterator() { // element iterator
return new QueueIterator();
}
/**
* Returns a nice string output of this queue.
* @return the Objects in FIFO order, separated by commas
*/
/* public String toString() { // return a string representation of the queue
// content
if (isEmpty()) {
return "";
}
String result = "<";
Node current = head;
while (current != null) {
result += current.data;
current = current.next;
if (current != null) {
result += ",";
}
}
return result + ">";
}
class QueueIterator implements Iterator<Object> {
private Node node = head; // First node is head
public Object next() {
Object val = node.data; // Read current value
node = node.next; // Move one step ahead
return val;
}
@Override
public boolean hasNext() {
return node != null;
}
}
}*/
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