java声明循环单链表类CircSinglyLinkedList，实现LList接口中的方法的代码

以下是Java代码实现：

public class CircSinglyLinkedList<E> implements LList<E> {

    private Node<E> tail;
    private int size;

    public CircSinglyLinkedList() {
        tail = null;
        size = 0;
    }

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

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

    @Override
    public boolean add(int index, E element) {
        if (index < 0 || index > size) {
            throw new IndexOutOfBoundsException("Index out of range: " + index);
        }
        Node<E> newNode = new Node<>(element);
        if (isEmpty()) {
            tail = newNode;
            tail.next = tail;
        } else if (index == 0) {
            newNode.next = tail.next;
            tail.next = newNode;
        } else if (index == size) {
            newNode.next = tail.next;
            tail.next = newNode;
            tail = newNode;
        } else {
            Node<E> prev = getNode(index - 1);
            newNode.next = prev.next;
            prev.next = newNode;
        }
        size++;
        return true;
    }

    @Override
    public boolean add(E element) {
        return add(size, element);
    }

    @Override
    public E remove(int index) {
        if (index < 0 || index >= size) {
            throw new IndexOutOfBoundsException("Index out of range: " + index);
        }
        E removedElement;
        if (size == 1) {
            removedElement = tail.element;
            tail = null;
        } else if (index == 0) {
            removedElement = tail.next.element;
            tail.next = tail.next.next;
        } else if (index == size - 1) {
            Node<E> prev = getNode(index - 1);
            removedElement = tail.element;
            prev.next = tail.next;
            tail = prev;
        } else {
            Node<E> prev = getNode(index - 1);
            removedElement = prev.next.element;
            prev.next = prev.next.next;
        }
        size--;
        return removedElement;
    }

    @Override
    public E get(int index) {
        if (index < 0 || index >= size) {
            throw new IndexOutOfBoundsException("Index out of range: " + index);
        }
        Node<E> node = getNode(index);
        return node.element;
    }

    @Override
    public int indexOf(E element) {
        if (isEmpty()) {
            return -1;
        }
        int index = 0;
        Node<E> node = tail.next;
        do {
            if (Objects.equals(element, node.element)) {
                return index;
            }
            node = node.next;
            index++;
        } while (node != tail.next);
        return -1;
    }

    @Override
    public E set(int index, E element) {
        if (index < 0 || index >= size) {
            throw new IndexOutOfBoundsException("Index out of range: " + index);
        }
        Node<E> node = getNode(index);
        E replacedElement = node.element;
        node.element = element;
        return replacedElement;
    }

    private Node<E> getNode(int index) {
        if (index == size - 1) {
            return tail;
        }
        Node<E> node = tail.next;
        for (int i = 0; i < index; i++) {
            node = node.next;
        }
        return node;
    }

    private static class Node<E> {
        E element;
        Node<E> next;

        Node(E element) {
            this.element = element;
        }
    }
}

上述代码中，我们实现了循环单链表类 `CircSinglyLinkedList<E>`，并实现了 `LList<E>` 接口中的方法。其中，我们使用了一个内部类 `Node<E>` 表示节点，每个节点包含一个元素和一个指向下一个节点的引用。类 `CircSinglyLinkedList<E>` 中的 `tail` 属性指向最后一个节点，因为这是循环单链表的特殊之处。通过这个属性，我们可以方便地实现在尾部添加元素和删除最后一个元素的方法。