JAVA学习（小白向）—循环队列—2021-06-06

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#java #队列

本文详细介绍了循环队列的原理，包括head和tail指针的作用，队列空的判断，以及如何在满队列和移除元素时进行操作。通过实例代码演示了队列的 enqueue 和 dequeue 方法，适合初学者理解 Java 循环队列的使用。

JAVA学习（小白向）—循环队列—2021-06-06

循环队列原理

head表示队列队首
tail表示队列队尾
当head=tail时表示队列为空
在该图这里插入图片描述
上图中front相当于代码里的head，此时队列为空。
当添加元素后，指针往后移动，执行tail++
在这里插入图片描述
当移除元素时，同理head指针往前移动，执行head++

代码

package a16;
/**
 * *******************************
 * Circle int queue.
 * @author hengyuzuo
 * *******************************
 */
public class CircleIntQueue {

	/**
	 * The total space. One space can never be used.
	 */
	public static final int TOTAL_SPACE = 10;

	/**
	 * The data.
	 */
	int[] data;

	/**
	 * The index of the head.
	 */
	int head;

	/**
	 * The index of the tail.
	 */
	int tail;

	/**
	 ******************* 
	 * The constructor
	 ******************* 
	 */
	public CircleIntQueue() {
		data = new int[TOTAL_SPACE];
		head = 0;
		tail = 0;
	}// Of the first constructor

	/**
	 *********************
	 * Enqueue.
	 * 
	 * @param paraValue
	 *            The value of the new node.
	 *********************
	 */
	public void enqueue(int paraValue) {
		if ((tail + 1) % TOTAL_SPACE == head) {
			System.out.println("Queue full.");
			return;
		} // Of if

		data[tail % TOTAL_SPACE] = paraValue;
		tail++;
	}// Of enqueue

	/**
	 *********************
	 * Dequeue.
	 * 
	 * @return The value at the head.
	 *********************
	 */
	public int dequeue() {
		if (head == tail) {
			System.out.println("No element in the queue");
			return -1;
		} // Of if

		int resultValue = data[head];

		head++;

		return resultValue;
	}// Of dequeue

	/**
	 *********************
	 * Overrides the method claimed in Object, the superclass of any class.
	 *********************
	 */
	public String toString() {
		String resultString = "";

		if (head == tail) {
			return "empty";
		} // Of if

		for (int i = head; i < tail; i++) {
			resultString += data[i % TOTAL_SPACE] + ", ";
		} // Of for i

		return resultString;
	}// Of toString

	/**
	 *********************
	 * The entrance of the program.
	 * 
	 * @param args
	 *            Not used now.
	 *********************
	 */
	public static void main(String args[]) {
		CircleIntQueue tempQueue = new CircleIntQueue();
		System.out.println("Initialized, the list is: " + tempQueue.toString());

		for (int i = 0; i < 5; i++) {
			tempQueue.enqueue(i + 1);
		} // Of for i
		System.out.println("Enqueue, the queue is: " + tempQueue.toString());

		int tempValue = tempQueue.dequeue();
		System.out.println("Dequeue " + tempValue + ", the queue is: " + tempQueue.toString());

		for (int i = 0; i < 6; i++) {
			tempQueue.enqueue(i + 10);
			System.out.println("Enqueue, the queue is: " + tempQueue.toString());
		} // Of for i

		for (int i = 0; i < 3; i++) {
			tempValue = tempQueue.dequeue();
			System.out.println("Dequeue " + tempValue + ", the queue is: " + tempQueue.toString());
		} // Of for i

		for (int i = 0; i < 6; i++) {
			tempQueue.enqueue(i + 100);
			System.out.println("Enqueue, the queue is: " + tempQueue.toString());
		} // Of for i
	}// Of main
}// Of CircleIntQueue

其中
循环队列的体现就在于，当10号位满了执行tail++时

	for (int i = head; i < tail; i++) {
			resultString += data[i % TOTAL_SPACE] + ", ";

能够通过求余总空间来将指针指向开头，当再继续添加元素求余时，head=tail，此时就满足满队列

	if ((tail + 1) % TOTAL_SPACE == head) {
			System.out.println("Queue full.");
			return;

运行结果

Initialized, the list is: empty
Enqueue, the queue is: 1, 2, 3, 4, 5, 
Dequeue 1, the queue is: 2, 3, 4, 5, 
Enqueue, the queue is: 2, 3, 4, 5, 10, 
Enqueue, the queue is: 2, 3, 4, 5, 10, 11, 
Enqueue, the queue is: 2, 3, 4, 5, 10, 11, 12, 
Enqueue, the queue is: 2, 3, 4, 5, 10, 11, 12, 13, 
Enqueue, the queue is: 2, 3, 4, 5, 10, 11, 12, 13, 14, 
Queue full.
Enqueue, the queue is: 2, 3, 4, 5, 10, 11, 12, 13, 14, 
Dequeue 2, the queue is: 3, 4, 5, 10, 11, 12, 13, 14, 
Dequeue 3, the queue is: 4, 5, 10, 11, 12, 13, 14, 
Dequeue 4, the queue is: 5, 10, 11, 12, 13, 14, 
Enqueue, the queue is: 5, 10, 11, 12, 13, 14, 100, 
Enqueue, the queue is: 5, 10, 11, 12, 13, 14, 100, 101, 
Enqueue, the queue is: 5, 10, 11, 12, 13, 14, 100, 101, 102, 
Queue full.
Enqueue, the queue is: 5, 10, 11, 12, 13, 14, 100, 101, 102, 
Queue full.
Enqueue, the queue is: 5, 10, 11, 12, 13, 14, 100, 101, 102, 
Queue full.
Enqueue, the queue is: 5, 10, 11, 12, 13, 14, 100, 101, 102,