循环队列的java实现

import java.util.Arrays;

public  class LoopQueue<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循环队列的元素
private Object[] elementData;
// 保存循环队列中元素的当前个数
private int front = 0;
private int rear = 0;

// 以默认数组长度创建空循环队列
public LoopQueue() {
capacity = DEFAULT_SIZE;
elementData = new Object[capacity];
}

// 以一个初始化元素来创建循环队列
public LoopQueue(T element) {
this();
elementData[0] = element;
rear++;
}

public LoopQueue(T element, int initSize) {
this.capacity = initSize;
elementData = new Object[capacity];
elementData[0] = element;
rear++;
}

// 获取循环队列的大小
public int length() {
if (empty()) {
return 0;
}
return rear > front ? rear - front : capacity - (front - rear);
}

// 插入队列
public void add(T element) {
if (rear == front && elementData[front] != null) {
throw new IndexOutOfBoundsException("队列已满的异常");
}
elementData[rear++] = element;
// 如果rear已经到头，那就转头
rear = rear == capacity ? 0 : rear;
}

// 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;
// 如果front已经到头，那就转头
front = front == capacity ? 0 : front;
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];
}

// 判断循环队列是否为空队列
public boolean empty() {
// rear==front且rear处的元素为null
return rear == front && elementData[rear] == null;
}

// 清空循环队列
public void clear() {
// 将底层数组所有元素赋为null
Arrays.fill(elementData, null);
front = 0;
rear = 0;
}

public String toString() {
if (empty()) {
return "[]";
} else {
// 如果front < rear，有效元素就是front到rear之间的元素
if (front < rear) {
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();
}
// 如果front >= rear，有效元素为front->capacity之间、0->front之间的
else {
StringBuilder sb = new StringBuilder("[");
for (int i = front; i < capacity; i++) {
sb.append(elementData[i].toString() + ", ");
}
for (int i = 0; i < rear; i++) {
sb.append(elementData[i].toString() + ", ");
}
int len = sb.length();
return sb.delete(len - 2, len).append("]").toString();
}
}
}
}