@SuppressWarnings("unchecked")
public class CircleDeque {
private int front;
private int size;
private E[] elements;
private static final int DEFAULT_CAPACITY = 10;

public CircleDeque() {  
    elements = (E\[\]) new Object\[DEFAULT\_CAPACITY\];  
}

public int size() {  
    return size;  
}

public boolean isEmpty() {  
    return size == 0;  
}

public void clear() {  
    for (int i = 0; i < size; i++) {  
        elements\[index(i)\] = null;  
    }  
    front = 0;  
    size = 0;  
}

/\*\*  
 \* 从尾部入队  
 \* @param element  
 \*/  
public void enQueueRear(E element) {  
    ensureCapacity(size + 1);

    elements\[index(size)\] = element;  
    size++;  
}

/\*\*  
 \* 从头部出队  
 \* @param element  
 \*/  
public E deQueueFront() {  
    E frontElement = elements\[front\];  
    elements\[front\] = null;  
    front = index(1);  
    size--;  
    return frontElement;  
}

/\*\*  
 \* 从头部入队  
 \* @param element  
 \*/  
public void enQueueFront(E element) {  
    ensureCapacity(size + 1);

    front = index(-1);  
    elements\[front\] = element;  
    size++;  
}

/\*\*  
 \* 从尾部出队  
 \* @param element  
 \*/  
public E deQueueRear() {  
    int rearIndex = index(size - 1);  
    E rear = elements\[rearIndex\];  
    elements\[rearIndex\] = null;  
    size--;  
    return rear;  
}

public E front() {  
    return elements\[front\];  
}

public E rear() {  
    return elements\[index(size - 1)\];  
}

@Override  
public String toString() {  
    StringBuilder string = new StringBuilder();  
    string.append("capcacity=").append(elements.length)  
    .append(" size=").append(size)  
    .append(" front=").append(front)  
    .append(", \[");  
    for (int i = 0; i < elements.length; i++) {  
        if (i != 0) {  
            string.append(", ");  
        }

        string.append(elements\[i\]);  
    }  
    string.append("\]");  
    return string.toString();  
}

private int index(int index) {  
    index += front;  
    if (index < 0) {  
        return index + elements.length;  
    }  
    return index - (index >= elements.length ? elements.length : 0);  
}

/\*\*  
 \* 保证要有capacity的容量  
 \* @param capacity  
 \*/  
private void ensureCapacity(int capacity) {  
    int oldCapacity = elements.length;  
    if (oldCapacity >= capacity) return;

    // 新容量为旧容量的1.5倍  
    int newCapacity = oldCapacity + (oldCapacity >> 1);  
    E\[\] newElements = (E\[\]) new Object\[newCapacity\];  
    for (int i = 0; i < size; i++) {  
        newElements\[i\] = elements\[index(i)\];  
    }  
    elements = newElements;

    // 重置front  
    front = 0;  
}  

}