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Xiaobian to share with you how Java to achieve circular queue, I hope you have something to gain after reading this article, let's discuss it together!

circular queue

Circular Queue is a special queue. Circular queue solves the problem of queue listing with O(n) complexity by moving all data forward one bit.

循环队列的底层依然是数组, 不过增加了指向头和尾的指针.

循环队列实现

判断队列是否为空: 当头指针 Q.front == 尾指针 Q.rear, 队列为空

判断队列是否为满: 当头指针 Q.front == 尾指针 Q.rear + 1) % Maxsize, 队列为满

改变队列大小// 改变队列大小private void resize(int capacity) { // 定义新数组 E[] newData = (E[]) new Object[capacity + 1]; // 转移数组元素 for (int i = 0; i < size; i++) { newData[i] = data[(i +front) % data.length]; } // 更新 data = newData; front = 0; rear = size;}enqueue 方法// 入队public void enqueue(E e) { // 判断是否为满 if((rear + 1) % data.length == front) { resize(getCapacity() * 2); } // 队伍加入 data[rear] = e; rear = (rear + 1) % data.length; size++;}dequeue 方法// 出队public E dequeue() { // 判断是否为空 if(isEmpty()) { throw new RuntimeException("队列为空"); } // 取出第一个元素 E element = data[front]; data[front] = null; // 移动头指针 front = (front + 1) % data.length; // 数组大小-1 size--; // 判断是否需要缩小 if(size==getCapacity() / 4 && getCapacity() / 2 != 0) { resize(getCapacity() / 2); } return element;}main// 主函数public static void main(String[] args) { // 创建循环队列 CircularQueue queue = new CircularQueue(5); // 入队 for (int i = 0; i < 8; i++) { queue.enqueue(i); System.out.println(queue); } // 出队 for (int i = 0; i < 8; i++) { queue.dequeue(); System.out.println(queue); }}

输出结果:

CircularQueue{data=[0, null, null, null, null, null], front=0, rear=1, size=1}

CircularQueue{data=[0, 1, null, null, null, null], front=0, rear=2, size=2}

CircularQueue{data=[0, 1, 2, null, null, null], front=0, rear=3, size=3}

CircularQueue{data=[0, 1, 2, 3, null, null], front=0, rear=4, size=4}

CircularQueue{data=[0, 1, 2, 3, 4, null], front=0, rear=5, size=5}

CircularQueue{data=[0, 1, 2, 3, 4, 5, null, null, null, null, null], front=0, rear=6, size=6}

CircularQueue{data=[0, 1, 2, 3, 4, 5, 6, null, null, null, null], front=0, rear=7, size=7}

CircularQueue{data=[0, 1, 2, 3, 4, 5, 6, 7, null, null, null], front=0, rear=8, size=8}

CircularQueue{data=[null, 1, 2, 3, 4, 5, 6, 7, null, null, null], front=1, rear=8, size=7}

CircularQueue{data=[null, null, 2, 3, 4, 5, 6, 7, null, null, null], front=2, rear=8, size=6}

CircularQueue{data=[null, null, null, 3, 4, 5, 6, 7, null, null, null], front=3, rear=8, size=5}

CircularQueue{data=[null, null, null, null, 4, 5, 6, 7, null, null, null], front=4, rear=8, size=4}

CircularQueue{data=[null, null, null, null, null, 5, 6, 7, null, null, null], front=5, rear=8, size=3}

CircularQueue{data=[6, 7, null, null, null, null], front=0, rear=2, size=2}

CircularQueue{data=[7, null, null], front=0, rear=1, size=1}

CircularQueue{data=[null, null], front=0, rear=0, size=0}

完整代码import java.util.ArrayList;import java.util.Arrays;public class CircularQueue { private E[] data; private int front, rear; private int size; // 无参构造 public CircularQueue() { this(10); } // 有参构造 public CircularQueue(int capacity) { data = (E[]) new Object[capacity + 1]; front = rear = size = 0; } // 入队 public void enqueue(E e) { // 判断是否为满 if((rear + 1) % data.length == front) { resize(getCapacity() * 2); } // 队伍加入 data[rear] = e; rear = (rear + 1) % data.length; size++; } // 出队 public E dequeue() { // 判断是否为空 if(isEmpty()) { throw new RuntimeException("队列为空"); } // 取出第一个元素 E element = data[front]; data[front] = null; // 移动头指针 front = (front + 1) % data.length; // 数组大小-1 size--; // 判断是否需要缩小 if(size==getCapacity() / 4 && getCapacity() / 2 != 0) { resize(getCapacity() / 2); } return element; } // 获取队列大小 public int getSize() { return size; } // 获取队列容量 public int getCapacity() { return data.length - 1; } // 队列是否为空 public boolean isEmpty() { return front == rear; } // 改变队列大小 private void resize(int capacity) { // 创建新数组 E[] newData = (E[]) new Object[capacity + 1]; // 转移数组元素 for (int i = 0; i < size; i++) { newData[i] = data[(i +front) % data.length]; } // 更新 data = newData; front = 0; rear = size; } @Override public String toString() { return "CircularQueue{" + "data=" + Arrays.toString(data) + ", front=" + front + ", rear=" + rear + ", size=" + size + '}'; } // 主函数 public static void main(String[] args) { // 创建循环队列 CircularQueue queue = new CircularQueue(5); // 入队 for (int i = 0; i < 8; i++) { queue.enqueue(i); System.out.println(queue); } // 出队 for (int i = 0; i < 8; i++) { queue.dequeue(); System.out.println(queue); } }}看完了这篇文章，相信你对"Java如何实现循环队列"有了一定的了解，如果想了解更多相关知识，欢迎关注行业资讯频道，感谢各位的阅读!

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