双链表实现不起作用

Question

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();
    }

}

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;
    }
}

能否有人请让我知道如果有任何问题与这个实现。

下面是我如何将节点添加到列表中：

DoublyLinkedList<Integer> mylist = new DoublyLinkedList<>();
DoublyLinkedListNode<Integer> node1 = new DoublyLinkedListNode<>(10);
DoublyLinkedListNode<Integer> node2= new DoublyLinkedListNode<>(20);
DoublyLinkedListNode<Integer> node3 = new DoublyLinkedListNode<>(30);
DoublyLinkedListNode<Integer> node4 = new DoublyLinkedListNode<>(40);
DoublyLinkedListNode<Integer> node5 = new DoublyLinkedListNode<>(50);
DoublyLinkedListNode<Integer> node6 = new DoublyLinkedListNode<>(60);
mylist.addNode(node1);
mylist.addNode(node2);
mylist.addNode(node3);
mylist.addNode(node4);
mylist.addNode(node5);
mylist.addNode(node6);
System.out.println(mylist.toString());

Answer 1

head引用并不总是null，它会在添加第一个节点时被初始化，这是traverseAndAdd（）方法代码中的问题。

private boolean traverseAndAdd(DoublyLinkedListNode<T> node) {
    boolean isAdded = false;
    while(null != head.getNext()) {
        if(head.getNext() == null) {
            //this code is unreachable
        }
        //why are u changing the head value
        head = head.getNext();
    }
    return isAdded;
}

因此将函数替换为

private void traverseAndAdd(DoublyLinkedListNode<T> node) {
    DoublyLinkedListNode<T>temp=head;
    while(null != temp.getNext()) {
        temp=temp.getNext();
    }
    temp.setNext(node);
    node.setPrev(temp);
}

另一个错误是，在toString（）方法中，您将空值赋给head。首先初始化head值，但每次调用toString（）时head值变为null。将方法替换为

public String toString() {
    StringBuffer sb = new StringBuffer();
    DoublyLinkedListNode<T>temp=head;
    while(null != temp) {
        sb.append(temp.getData());
        temp = temp.getNext();
    }
    return sb.toString();
}