Java/DataStructures/Queues/Queues.java at master · loisoft/Java · GitHub

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package DataStructures.Queues;

/**

* This implements Queues by using the class Queue.

* <p>A queue data structure functions the same as a real world queue. The elements that are added

* first are the first to be removed. New elements are added to the back/rear of the queue.

class Queue {

/** Default initial capacity. */

private static final int DEFAULT_CAPACITY = 10;

/** Max size of the queue */

private int maxSize;

/** The array representing the queue */

private int[] queueArray;

/** Front of the queue */

private int front;

/** Rear of the queue */

private int rear;

/** How many items are in the queue */

private int nItems;

/** init with DEFAULT_CAPACITY */

public Queue() {

this(DEFAULT_CAPACITY);

}

/**

* Constructor

* @param size Size of the new queue

public Queue(int size) {

maxSize = size;

queueArray = new int[size];

front = 0;

rear = -1;

nItems = 0;

}

/**

* Inserts an element at the rear of the queue

* @param x element to be added

* @return True if the element was added successfully

public boolean insert(int x) {

if (isFull()) return false;

// If the back of the queue is the end of the array wrap around to the front

rear = (rear + 1) % maxSize;

queueArray[rear] = x;

nItems++;

return true;

}

/**

* Remove an element from the front of the queue

* @return the new front of the queue

public int remove() {

if (isEmpty()) {

return -1;

}

int temp = queueArray[front];

front = (front + 1) % maxSize;

nItems--;

return temp;

}

/**

* Checks what's at the front of the queue

* @return element at the front of the queue

public int peekFront() {

return queueArray[front];

}

/**

* Checks what's at the rear of the queue

* @return element at the rear of the queue

public int peekRear() {

return queueArray[rear];

}

/**

* Returns true if the queue is empty

* @return true if the queue is empty

public boolean isEmpty() {

return nItems == 0;

}

/**

* Returns true if the queue is full

* @return true if the queue is full

public boolean isFull() {

return nItems == maxSize;

}

/**

* Returns the number of elements in the queue

* @return number of elements in the queue

public int getSize() {

return nItems;

}

@Override

public String toString() {

StringBuilder sb = new StringBuilder();

sb.append("[");

for (int i = front; ; i = ++i % maxSize) {

sb.append(queueArray[i]).append(", ");

if (i == rear) {

break;

}

sb.replace(sb.length() - 2, sb.length(), "]");

return sb.toString();

}

/**

* This class is the example for the Queue class

* @author Unknown

public class Queues {

/**

* Main method

* @param args Command line arguments

public static void main(String[] args) {

Queue myQueue = new Queue(4);

myQueue.insert(10);

myQueue.insert(2);

myQueue.insert(5);

myQueue.insert(3);

// [10(front), 2, 5, 3(rear)]

System.out.println(myQueue.isFull()); // Will print true

myQueue.remove(); // Will make 2 the new front, making 10 no longer part of the queue

// [10, 2(front), 5, 3(rear)]

myQueue.insert(7); // Insert 7 at the rear which will be index 0 because of wrap around

Java/DataStructures/Queues/Queues.java at master · loisoft/Java · GitHub

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