Question

我正在尝试对我的DSALinkedList进行单元测试，但是当我的removeFirst()方法失败时，它会出现。我无法弄明白为什么。有人可以帮我吗？

或者我在removeFirst()以外的其他地方出错了？请帮忙！！谢谢你提前！

这是我的DSALinkedList

public class DSALinkedList {

    public DSAListNode head;
    public DSAListNode tail;
    Object[] newValue;

public DSALinkedList(){
    head = null;
    tail = null;
    }

public void insertFirst(Object newValue){
    DSAListNode newNd;
    newNd = new DSAListNode(newValue);
    if (head == null) {
    head = newNd;
    tail = newNd;   
    }
    else{
    newNd.setNext(head);
    head = newNd;
    }
}
public void insertLast(Object newValue){
    DSAListNode newNd;
    newNd = new DSAListNode(newValue);
    if(head == null){
    head = newNd;
     }
    else {
    tail.next = newNd;
    tail = newNd;   
    }
}

public boolean isEmpty() {
     return (head == null);
 }

public Object peekFirst(){
    Object nodeValue;
    if (head == null)
    throw new IllegalArgumentException("head is empty");

    else 
    nodeValue = head.getValue();

   return nodeValue;
}

public Object peekLast(){
    Object nodeValue;
    if (head == null)
    throw new IllegalArgumentException("head is empty");
    else
    nodeValue = tail.getValue();
    return nodeValue;
}
public Object removeFirst(){
   Object nodeValue;
    if (head == null)
    throw new IllegalArgumentException("head is empty");        
    else 
    nodeValue = head.getValue();
    head = head.getNext();
    return nodeValue;
}
}

Answer 1

首先删除时，有一个边缘情况（当head == tail时）你需要更新头部和尾部。

我怀疑你的单元测试在单次插入后失败，然后从每一端连续移除一次。第二个请求应该抛出一个异常，因为deque现在是空的。

Answer 2

我发现有两个地方没有处理@Chris提到的需要改进的边缘情况，请参阅评论。

public void insertLast(Object newValue) {
    DSAListNode newNd;
    newNd = new DSAListNode(newValue);
    if (head == null) {
        head = newNd;
        tail = newNd; // this should be added
    } else {
        tail.next = newNd;
        tail = newNd;
    }
}

和此：

public Object removeFirst() {
    Object nodeValue;
    if (head == null) {
        throw new IllegalArgumentException("head is empty");
    } else {
        nodeValue = head.getValue();
    }

    head = head.getNext();
    // the following block should be added
    if (head == null) {
        tail = null;
    }
    return nodeValue;
}

JAVA双重LinkedList - 单元测试失败

2 个答案: