【数据结构】队列之顺序队列

public class SequenceQueue<T> {

    private int DEFAULT_SIZE = 10;
    // 保存数组的长度
    private int capacity;
    // 定义一个数组用于保存顺序队列的元素
    private Object[] elementData;
    // 保存顺序队列中元素的当前个数
    private int front = 0;
    private int rear  = 0;
    // 以默认数组长度建立空顺序队列
    public SequenceQueue() {
        capacity = DEFAULT_SIZE;
        elementData = new Object[capacity];
    }
    // 以一个初始化元素来建立顺序队列
    public SequenceQueue(T element) {
        this();
        elementData[0] = element;
        rear++;
    }
    /**
     * 以指定长度的数组来建立顺序队列
     * @param element 指定顺序队列中第一个元素
     * @param initSize 指定顺序队列底层数组的长度
     */
    public SequenceQueue(T element, int initSize) {
        this.capacity = initSize;
        elementData = new Object[capacity];
        elementData[0] = element;
        rear++;
    }
    // 获取顺序队列的大小
    public int length() {
        return rear -front;
    }
    // 判断顺序队列是否为空队列
    public boolean empty() {
        return rear == front;
    }
    // 插入队列
    public void add(T element) {
        if (rear > capacity - 1) {
            throw new IndexOutOfBoundsException("队列已满的异常");
        }
        elementData[rear++] = element;
    }
    // 移除队列
    public T remove() {
        if (empty()) {
            throw new IndexOutOfBoundsException("空队列异常");
        }
        // 保留队列的rear端的元素的值
        T oldValue = (T)elementData[front];
        // 释放队列的rear端的元素
        elementData[front++] = null;
        return oldValue;
    }
    // 返回队列顶元素，但不删除队列顶元素
    public T element() {
        if (empty()) {
            throw new IndexOutOfBoundsException("空队列异常");
        }
        return (T)elementData[front];
    }
    // 清空顺序队列
    public void clear() {
        Arrays.fill(elementData, null);
        front = 0;
        rear  = 0;
    }
    public String toString() {
        if (empty()) {
            return "[]";
        } else {
            StringBuilder sb = new StringBuilder("[");
            for (int i = front; i < rear; i++) {
                sb.append(elementData[i].toString() + ", ");
            }
            int len = sb.length();
            return sb.delete(len - 2, len).append("]").toString();
        }
    }
}

public class SequenceQueueTest {
    public static void main(String[] args) {
        SequenceQueue<String> queue = new SequenceQueue<String>();
        queue.add("aaaa");
        queue.add("bbbb");
        queue.add("cccc");
        queue.add("dddd");
        System.out.println("顺序队列初始化元素：" + queue.toString());
        System.out.println("访问顺序队列的front端元素：" + queue.element());
        System.out.println("移除顺序队列的front端元素：" + queue.remove());
        System.out.println("第一次移除front端元素后：" + queue.toString());
        System.out.println("移除顺序队列的front端元素：" + queue.remove());
        System.out.println("第二次移除front端元素后：" + queue.toString());
    }
}