Java Queue-数组队列和循环队列-学习记录

package queue;

import array.Array;

/**
 * @Title: ArrayQueue
 * @ProjectName Demo03
 * @date 2018/9/1214:09
 */
public class ArrayQueue<E> implements Queue<E> {
    private Array<E> array;
    public ArrayQueue() {
        array = new Array<>();
    }
    public ArrayQueue(int capacity) {
        array = new Array<>(capacity);
    }
    @Override
    public int getSize() {
        return array.getSize();
    }

    @Override
    public boolean isEmpty() {
        return array.isEmpty();
    }

    @Override
    public void enqueue(E e) {
        array.addLast(e);
    }

    @Override
    public E dequeue() {
        return array.removeFirst();
    }

    @Override
    public E getFront() {
        return array.getFirst();
    }

    @Override
    public String toString() {
        StringBuilder res = new StringBuilder();
        res.append("Queue:");
        res.append("Front [");
        for (int i = 0; i < array.getSize(); i++) {
            res.append(array.get(i));
            if (i != array.getSize() - 1) {
                res.append(",");
            }
        }
        res.append("] tail");
        return res.toString();
    }

    public static void main(String[] args) {
        ArrayQueue<String> arrayQueue = new ArrayQueue<>();
        arrayQueue.enqueue("1");
        arrayQueue.enqueue("2");
        System.out.println(arrayQueue);
        System.out.println(arrayQueue.getFront());
        arrayQueue.dequeue();
        System.out.println(arrayQueue);
    }
}

　

package queue;

/**
 * @Title: LoopQueue
 * @ProjectName Demo03
 * @date 2018/9/1214:17
 */
public class LoopQueue<E> implements Queue<E> {
    private E[] data;
    // 元素所在位置,元素入队下一个位置
    private int front, tail;
    private int size;

    public LoopQueue(int capacity) {
        data = (E[]) new Object[capacity + 1];
        front = 0;
        tail = 0;
        size = 0;
    }

    public LoopQueue() {
        this(10);
    }

    @Override
    public int getSize() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return front == tail;
    }

    public int getCapacity() {
        return data.length - 1;
    }

    @Override
    public void enqueue(E e) {
        if ((tail + 1) % data.length == front) {
            // 队列已满
            resize(getCapacity() * 2);
        }
        data[tail] = e;
        tail = (tail + 1) % data.length;
        size++;
    }

    @Override
    public E dequeue() {
        if (isEmpty()) {
            throw new IllegalArgumentException("队列为空");
        }
        E e = data[front];
        front = (front + 1) % data.length;
        size--;
        if (size == getCapacity() / 4 && getCapacity() / 2 != 0) {
            resize(getCapacity() / 2);
        }
        return e;
    }

    @Override
    public E getFront() {
        if (isEmpty()) {
            throw new IllegalArgumentException("队列为空");
        }
        return data[front];
    }

    private void resize(int capacity) {
        E[] newData = (E[]) new Object[capacity + 1];
        for (int i = 0; i < size; i++) {
            newData[i] = data[(i + front) % data.length];
        }
        data = newData;
        front = 0;
        tail = size;
    }

    @Override
    public String toString() {
        StringBuilder res = new StringBuilder();
        res.append(String.format("LoopQueue: size=%d , capacity=%d
", size, getCapacity()));
        res.append("Front: [");
        for (int i = front; i != tail; i = (i + 1) % data.length) {
            res.append(data[i]);
            if ((i + 1) % data.length != tail)
                res.append(',');
        }
        res.append("] tail");
        return res.toString();
    }
    public static void main(String[] args){

        LoopQueue<Integer> queue = new LoopQueue<>(5);
        for(int i = 0 ; i < 10 ; i ++){
            queue.enqueue(i);
            System.out.println(queue);

            if(i % 3 == 2){
                queue.dequeue();
                System.out.println(queue);
            }
        }
    }
}