《Java数据结构与算法》笔记-CH4-4循环队列

/**
 * 循环队列
 */
class Queue {
	private int maxSize;
	private long[] queue;
	private int front;
	private int rear;
	private int nItems;

	public Queue(int size) {
		maxSize = size;
		queue = new long[maxSize];
		front = 0;
		rear = -1;
		nItems = 0;
	}

	/**
	 * 插入value 运行的前提条件是队列不满。满的话抛出异常
	 * 
	 * @param value
	 * @throws Exception
	 */
	public void insert(long value) throws Exception {
		if (isFull()) {
			throw new Exception("queue is full, can not insert " + value);
		}
		// 当rear指针指向数组的顶端，即maxSize-1位置时，在插入数据项之前，必须绕回到数组的底端。
		// 回绕操作把rear设置为-1，因此当rear加1后为0，是数组底端的下标值
		if (rear == maxSize - 1) {
			rear = -1;
		}
		// 插入操作rear队尾指针加一后，在队尾指针所指的位置处插入新的数据。然后nItem++
		queue[++rear] = value;
		nItems++;
	}

	/**
	 * 队头移除操作 前提是队列不空，为空则抛出异常
	 * 
	 * @return
	 * @throws Exception
	 */
	public long remove() throws Exception {
		if (isEmpty()) {
			throw new Exception("queue is empty, can not remove");
		}
		// 移除操作总是由front指针得到队头数据项的值，然后将front加一。
		long temp = queue[front++];
		// 如果进行完毕后front的值超过数组的顶端，也就是==maxSize，front就必须绕回到0位置
		if (front == maxSize)
			front = 0;
		// 操作完毕后，nItems减一
		nItems--;
		return temp;
	}

	public long peekFront() {
		return queue[front];
	}

	public boolean isEmpty() {
		return nItems == 0;
	}

	public boolean isFull() {
		return nItems == maxSize;
	}

	public int size() {
		return nItems;
	}
}

public class QueueDemo {
	public static void main(String[] args) {
		Queue q = new Queue(5);
		try {
			for (int i = 0; i < 7; i++) {
				q.insert(i);
			}
		} catch (Exception e) {
			System.out.println(e);
		}

		try {
			for (int i = 0; i < 7; i++) {
				System.out.println("removed " + q.remove() + ", and queue size is: " + q.size());
			}
		} catch (Exception e) {
			System.out.println(e);
		}

	}
}