我有一個(gè)雙重鏈表實(shí)現(xiàn)如下：public class DoublyLinkedList<T> {    DoublyLinkedListNode<T> head;    public DoublyLinkedListNode<T> getHead() {        return head;    }    public void setHead(DoublyLinkedListNode<T> head) {        this.head = head;    }    public void addNode(DoublyLinkedListNode<T> node) {        if(null == head) {            head = new DoublyLinkedListNode<>(node.getData());        }else{            traverseAndAdd(node);        }    }    private boolean traverseAndAdd(DoublyLinkedListNode<T> node) {         boolean isAdded = false;    DoublyLinkedListNode<T> tempHead = head;  do{        if(tempHead.getNext() == null) {            head.setNext(node);            node.setPrev(head);            isAdded = true;            break;        }         tempHead = tempHead.getNext();    }while(null != tempHead);    return isAdded;    }    @Override    public String toString() {        StringBuffer sb = new StringBuffer();        while(null != head) {            sb.append(head.getData());            head = head.getNext();        }        return sb.toString();    }}以下是我的DoubleLinkedListNode類：public class DoublyLinkedListNode<T> {    T data;    DoublyLinkedListNode<T> prev;    DoublyLinkedListNode<T> next;    public DoublyLinkedListNode(T data) {        this.data = data;    }    public T getData() {        return data;    }    public void setData(T data) {        this.data = data;    }    public DoublyLinkedListNode<T> getPrev() {        return prev;    }    public void setPrev(DoublyLinkedListNode<T> prev) {        this.prev = prev;    }    public DoublyLinkedListNode<T> getNext() {        return next;    }    public void setNext(DoublyLinkedListNode<T> next) {        this.next = next;    }}現(xiàn)在，當(dāng)我創(chuàng)建DoublyLinkedList的實(shí)例并嘗試以某種方式向其添加節(jié)點(diǎn)時(shí)，我的頭部實(shí)例變量始終為空。即使我在addNode方法中初始化它，當(dāng)我嘗試添加下一個(gè)節(jié)點(diǎn)時(shí)，它總是空的。如果有人知道這個(gè)實(shí)現(xiàn)有任何問(wèn)題，有人可以告訴我。