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Queues.java
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158 lines (144 loc) · 3.6 KB
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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.
*
* @author Unknown
*/
class Queue {
/**
* 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;
/**
* 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 (rear == maxSize - 1) // If the back of the queue is the end of the array wrap around to the front
rear = -1;
rear++;
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() { // Remove an element from the front of the queue
if (isEmpty()) {
System.out.println("Queue is empty");
return -1;
}
int temp = queueArray[front];
front++;
if (front == maxSize) //Dealing with wrap-around again
front = 0;
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;
}
}
/**
* 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
// [7(rear), 2(front), 5, 3]
System.out.println(myQueue.peekFront()); // Will print 2
System.out.println(myQueue.peekRear()); // Will print 7
}
}