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FixedSizeArrayQueue.java
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/
FixedSizeArrayQueue.java
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package com.hrishikeshmishra.ns.queue;
import java.util.StringJoiner;
/**
* Problem
* Fixed size array queue using circular array to optimize memory.
*
* @author hrishikesh.mishra
* @link http://hrishikeshmishra.com/fixed-size-array-based-queue/
*/
public class FixedSizeArrayQueue<E> implements Queue<E> {
private E[] repository;
private int front, rear;
private int size;
private int capacity;
public FixedSizeArrayQueue(int capacity) {
this.size = 0;
this.rear = 0;
this.front = 0;
this.capacity = capacity;
this.repository = (E[]) new Object[capacity];
}
public FixedSizeArrayQueue() {
this(8);
}
@Override
public void enQueue(E element) {
if (size == repository.length)
throw new RuntimeException("Queue is full.");
this.repository[this.rear] = element;
this.rear = (this.rear + 1) % capacity;
this.size++;
}
@Override
public E deQueue() {
if (this.size == 0)
throw new RuntimeException("Queue is empty.");
E data = this.repository[this.front];
this.repository[this.front] = null;
this.front = (this.front + 1) % capacity;
this.size--;
return data;
}
@Override
public E front() {
if (this.size == 0)
throw new RuntimeException("Queue is empty.");
return this.repository[this.front];
}
@Override
public int size() {
return size;
}
@Override
public boolean isEmpty() {
return (size == 0);
}
@Override
public String toString() {
StringJoiner joiner = new StringJoiner(", ", "[", "]");
if (!isEmpty())
for (int j = 0; j < size; j++)
joiner.add(String.valueOf(this.repository[((front + j) % capacity)]));
return joiner.toString();
}
}
class FixedSizeArrayQueueTest {
public static void main(String[] args) {
Queue<Integer> queue = new FixedSizeArrayQueue<Integer>(4);
queue.enQueue(1);
queue.enQueue(2);
queue.enQueue(3);
System.out.println("Queue after enqueue (1, 2, 3) : " + queue);
System.out.println("Queue after dequeue : " + queue.deQueue() + ", Queue: " + queue);
System.out.println("Queue after dequeue : " + queue.deQueue() + ", Queue: " + queue);
queue.enQueue(4);
queue.enQueue(5);
System.out.println("Queue after dequeue : " + queue.deQueue() + ", Queue: " + queue);
queue.enQueue(6);
System.out.println("Queue after dequeue : " + queue.deQueue() + ", Queue: " + queue);
System.out.println("Queue after dequeue : " + queue.deQueue() + ", Queue: " + queue);
System.out.println("Queue after dequeue : " + queue.deQueue() + ", Queue: " + queue);
}
}