Java实现循环队列

数组实现

public class Queue_<T> {

	// 循环队列的数组
    private Object[] object;
    // 首指针
    private int front;
    // 尾指针
    private int rear;

    public Queue_() {
        object = new Object[20];
        front = rear = 0;
    }

	// 从尾部向队列添加元素
    public void enQueue(int value) {
        if (isFull()) {
            throw new OutOfMemoryError();
        } else {
            object[rear] = value;
            rear = (rear + 1) % 20;
        }
    }

	// 从首部删除队列元素
    public void deQueue() {
        if (isEmpty()) {
            throw new NullPointerException();
        } else {
            front = (front + 1) % 20;
        }
    }

	// 返回队首元素
    public T Front() {
        if (isEmpty()) return null;
        else
            return (T) object[front];
    }

	// 返回队尾元素
    public T Rear() {
        if (isEmpty()) return null;
        else
            return (T) object[(rear - 1 + 20) % 20];
    }

	// 判断队列是否为空
    public boolean isEmpty() {
        return (rear == front);
    }

	// 判断队列是否已满
    public boolean isFull() {
        return (rear + 1) % 20 == front;
    }

	// 返回队列长度
    public int size() {
        return (rear - front + 20) % 20;
    }
}

Java实现链式对联

内部类实现

public class Queue_plus<T> {

	// 节点
    private class queue<T> {
        Object object;
        queue next;
    }

	// 首指针
    queue<T> front;
    // 尾指针
    queue<T> rear;
    int size;

    public Queue_plus() {
        front = rear = null;
    }

	// 从队列尾部添加元素
    public void enQueue(T t) {
        if (t == null) {
            throw new NullPointerException();
        }
        if (front == null) {
            front = rear = new queue<T>();
            front.object = t;
            front.next = null;
        } else {
            rear.next = new queue<T>();
            rear = rear.next;
            rear.object = t;
            rear.next = null;
        }
    }

	// 从队列首部删除元素
    public void deQueue() {
        if (!isEmpty())
            front = front.next;
        else throw new NullPointerException();
    }

	// 返回队首元素
    public T Front() {
        return (T) front.object;
    }

	// 返回队尾元素
    public T Rear() {
        return (T) rear.object;
    }

	// 判断队列是否为空
    public boolean isEmpty() {
        if (front == null) {
            return true;
        } else return false;
    }

	// 返回队列长度
    public int size() {
        return size;
    }
}

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