写一个循环队列

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package structures;

public class LoopQueue<E> implements Queue<E> {

    private E[] data;
    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);
    }

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

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

    @Override
    public E getFront() {
        if (isEmpty()) {
            throw new IllegalArgumentException("the queue is empty");
        }

        return data[front];
    }

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

    @Override
    public void enqueue(E e) {
        //判断队列是否满了
        if ((tail + 1) % data.length == front) {
            resize(getCapacity() * 2);
        }

        data[tail] = e;
        tail = (tail + 1) % data.length;
        size ++;
    }

    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 E dequeue() {
        if (isEmpty()) {
            throw new IllegalArgumentException("queue is empty");
        }

        E res = data[front];
        front = (front + 1) % data.length;
        size --;

        if (size == getCapacity() / 4 && getCapacity() / 2 != 0) {
            resize(getCapacity() / 2);
        }

        return res;
    }

    @Override
    public String toString() {
        StringBuffer stringBuffer = new StringBuffer();
        stringBuffer.append(String.format("LoopQueue: size = %d\ncapacity = %d\n", size, getCapacity()));
        stringBuffer.append("front [");
        for (int i = front; i != tail; i = (i + 1) % data.length) {
            stringBuffer.append(data[i]);
            if (tail != (i + 1) % data.length) {
                stringBuffer.append(',');
            }
        }

        stringBuffer.append("] tail\n");


        return stringBuffer.toString();
    }
}

测试效率

package structures;

import java.util.Random;

public class Main {
    public static void main(String[] args) {
        LoopQueue<Integer> loopQueue = new LoopQueue<>();
        ArrayQueue<Integer> arrayQueue = new ArrayQueue<>();

        double test1 = test(loopQueue, 100000);
        double test2 = test(arrayQueue, 100000);

        System.out.println(test1);
        System.out.println(test2);
    }

    public static double test(Queue<Integer> q, int count) {
        long start = System.nanoTime();
        Random random = new Random();
        for (int i = 0; i < count; i++) {
            q.enqueue(random.nextInt(Integer.MAX_VALUE));
        }

        for (int i = 0; i < count; i++) {
            q.dequeue();
        }

        long stop = System.nanoTime();

        return (stop - start) / 1000000000.0;
    }
}