csci1913/lab10.java

//  ARRAY QUEUE. A fixed length queue implemented as a circular array.

class ArrayQueue <Base> {
	private int front; //  Index of front object in OBJECTS.
	private int rear; //  Index obf rear object in OBJECTS.
	private Base[] objects; //  The objects in the queue.
	
	public class Iterator {
		private ArrayQueue<Base> parent;
		private int position;
		public Iterator(ArrayQueue<Base> parent) {
			this.parent = parent;
			this.position = 0;
		}
		public boolean hasNext() {
			int _rear = parent.rear - parent.front;
			if (_rear < 0) _rear += parent.objects.length;
			return this.position < _rear;
		}
		public Base next() {
			return parent.objects[(parent.front + ++this.position) % parent.objects.length];
		}
	}
	
	public Iterator iterator() {
		return new Iterator(this);
	}

	//  Constructor. Make a new empty queue that can hold SIZE - 1 elements.

	public ArrayQueue(int size) {
		if (size >= 1) {
			front = 0;
			rear = 0;
			objects = (Base[]) new Object[size];
		} else {
			throw new IllegalArgumentException("Size must be at least one.");
		}
	}

	//  IS EMPTY. Test if the queue is empty.

	public boolean isEmpty() {
		return front == rear;
	}

	//  IS FULL. Test if the queue can hold no more elements.

	public boolean isFull() {
		return front == (rear + 1) % objects.length;
	}

	//  ENQUEUE. Add OBJECT to the rear of the queue.

	public void enqueue(Base object) {
		int nextRear = (rear + 1) % objects.length;
		if (front == nextRear) {
			throw new IllegalStateException("Queue is full.");
		} else {
			rear = nextRear;
			objects[rear] = object;
		}
	}

	//  DEQUEUE. Remove an object from the front of the queue and return it.

	public Base dequeue() {
		if (isEmpty()) {
			throw new IllegalStateException("Queue is empty.");
		} else {
			front = (front + 1) % objects.length;
			Base temp = objects[front];
			objects[front] = null;
			return temp;
		}
	}
}

class lab10 {

	//  MAIN. Start execution here.  

	public static void main(String[] args) {

		//  Make an ARRAY QUEUE and enqueue some things.  

		ArrayQueue<String> queue = new ArrayQueue<String>(5);
		queue.enqueue("A");
		queue.enqueue("B");
		queue.enqueue("C");

		//  Make an ITERATOR for QUEUE.  

		ArrayQueue<String>.Iterator first = queue.iterator();
		while (first.hasNext()) {
			System.out.println(first.next()); //  Print A B C, one per line.  
		}

		//  The iterator hasn’t changed QUEUE!.  

		System.out.println(queue.isEmpty()); //  Print false  
		System.out.println(queue.dequeue()); //  Print A  
		System.out.println(queue.dequeue()); //  Print B  
		System.out.println(queue.dequeue()); //  Print C  
		System.out.println(queue.isEmpty()); //  Print true  

		//  Let’s enqueue more things to QUEUE.  

		queue.enqueue("X");
		queue.enqueue("Y");
		queue.enqueue("Z");

		//  Now make a SECOND ITERATOR for QUEUE. The FIRST one won’t work any more.  

		ArrayQueue<String>.Iterator second = queue.iterator();
		while (second.hasNext()) {
			System.out.println(second.next()); //  Print X Y Z, one per line.  
		}

		//  The SECOND iterator hasn’t changed QUEUE either!  

		System.out.println(queue.isEmpty()); //  Print false  
		System.out.println(queue.dequeue()); //  Print X  
		System.out.println(queue.dequeue()); //  Print Y  
		System.out.println(queue.dequeue()); //  Print Z  
		System.out.println(queue.isEmpty()); //  Print true  
	}
}