我得到了这个赋值，为双向链表创建了一个equals方法。到目前为止，我得到了下面发布的代码。它通过了一些测试，但不是全部。失败确实与实际值具有相同的期望值，但我仍然得到一些AssertionErrors。
我一直在搞乱并试图改变一段时间，但我似乎无法自己解决这个问题。我也无法在互联网上找到任何好的例子。我已经尝试使用Eclipse生成equals方法，但这也没有通过所有测试。
我知道你不会在这里泄露免费的答案，但有人可能会指出代码中的错误吗？
/**
* This method should return true iff the values of this list
* and that are identical and in the same order.
* @param that list to compare this to.
* @return true iff the values are identical and in the same order
*/
public boolean equals(Object that) {
if (that == null)
return false;
if (!(that instanceof DoublyLinkedList) )
return false;
DoublyLinkedList<E> other = (DoublyLinkedList<E>) that;
if (header == null&&other.header != null)
return false;
if (trailer == null&&other.trailer != null)
return false;
while (header.getNext() != trailer){
if (!(header.equals(other.header))){
return false;
}
header = header.getNext();
other.header = other.header.getNext();
}
return true;
}
根据请求编辑DLL类的失败测试：
public static class DoublyLinkedList<E> {
private Node<E> header;
private Node<E> trailer;
/**
* Constructor that creates an empty DLL
*/
public DoublyLinkedList() {
this.header = new Node<>(null, null, null);
this.trailer = new Node<>(null, header, null);
this.header.setNext(trailer);
}
/**
* @return if the list is empty.
*/
public boolean isEmpty() {
return this.header.getNext() == this.trailer;
}
/**
* @return the first element of the list.
*/
public E getFirst() {
if (isEmpty()) return null;
return this.header.getNext().getElement();
}
/**
* @return the last element of the list.
*/
public E getLast() {
if (isEmpty()) return null;
return this.trailer.getPrevious().getElement();
}
/**
* Adds a new Node to the beginning of the list,
* containing the specified value.
* @param value for the new first node to hold.
*/
public void addFirst(E element) {
Node<E> newNode = new Node<>(element, header, header.getNext());
header.getNext().setPrevious(newNode);
header.setNext(newNode);
}
/**
* This method should return true iff the values of this list
* and that are identical and in the same order.
* @param that list to compare this to.
* @return true iff the values are identical and in the same order
*/
public boolean equals(Object that) {
if (that == null)
return false;
if (!(that instanceof DoublyLinkedList) )
return false;
DoublyLinkedList<E> other = (DoublyLinkedList<E>) that;
if (header == null&&other.header != null)
return false;
if (trailer == null&&other.trailer != null)
return false;
while (header.getNext() != trailer){
if (!(header.equals(other.header))){
return false;
}
header = header.getNext();
other.header = other.header.getNext();
}
return true;
}
/**
* Simple toString for testing purposes. Please note that solutions that use the
* .toString() to implement the .equals() method will be rejected.
*/
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append("DoublyLinkedList<");
Node<E> finger = header.getNext();
while (finger != trailer) {
sb.append(finger.toString());
if (finger.getNext() != trailer) {
sb.append("-");
}
finger = finger.getNext();
}
sb.append(">");
return sb.toString();
}
}
测试：
@Test
public void testEqualsCopy() {
Solution.DoublyLinkedList<Integer> dll1 = createDLL(2);
Solution.DoublyLinkedList<Integer> dll2 = createDLL(2);
assertEquals(dll1, dll2);
}
@Test
// Both lists contain only the entry 42.
public void testTwoEqualLists() {
Solution.DoublyLinkedList<Integer> dll1 = new Solution.DoublyLinkedList<>();
Solution.DoublyLinkedList<Integer> dll2 = new Solution.DoublyLinkedList<>();
dll1.addFirst(42);
dll2.addFirst(42);
assertEquals(dll1, dll2);
}
和错误：
testEqualsCopy(UTest) failed: 'java.lang.AssertionError: expected: Solution$DoublyLinkedList<DoublyLinkedList<1-0>> but was: Solution$DoublyLinkedList<DoublyLinkedList<1-0>>'
testTwoEqualLists(UTest) failed: 'java.lang.AssertionError: expected: Solution$DoublyLinkedList<DoublyLinkedList<42>> but was: Solution$DoublyLinkedList<DoublyLinkedList<42>>'
答案 0 :(得分：2)
因为，我认为双链表应该看起来和你有什么之间存在相当大的差距，我想添加我的示例实现。它取消了IMHO根本不需要的虚拟标题和预告片节点。
public class DoublyLinkedList<E> {
private Node<E> header;
private Node<E> trailer;
/**
* @return if the list is empty.
*/
public boolean isEmpty() {
return header == null;
}
/**
* @return the first element of the list.
*/
public E getFirst() {
return header != null ? header.getElement() : null;
}
/**
* @return the last element of the list.
*/
public E getLast() {
return trailer != null ? trailer.getElement() : null;
}
/**
* Adds a new Node to the beginning of the list,
* containing the specified value.
* @param value for the new first node to hold.
*/
public void addFirst(E element) {
Node<E> newNode = new Node<E>(element, null, header);
header = newNode;
if (trailer == null) {
trailer = newNode;
}
}
/**
* This method should return true if the values of this list and that are
* identical and in the same order.
*
* @param that
* list to compare this to.
* @return true if the values are identical and in the same order
*/
@SuppressWarnings("unchecked")
public boolean equals(Object that) {
if (!(that instanceof DoublyLinkedList))
return false;
DoublyLinkedList<E> other = (DoublyLinkedList<E>) that;
// if lists are empty
if (header == null) {
return other.header == null ? true : false;
}
if (!header.equals(other.header))
return false;
// Just one element
if (header == trailer) {
return true;
}
if (!trailer.equals(other.trailer))
return false;
Node<E> thisNode = header;
Node<E> otherNode = other.header;
while (thisNode.getNext() != trailer) {
thisNode = thisNode.getNext();
otherNode = otherNode.getNext();
if (!(thisNode.equals(otherNode))) {
return false;
}
}
return true;
}
/**
* Simple toString for testing purposes. Please note that solutions that use the
* .toString() to implement the .equals() method will be rejected.
*/
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append("DoublyLinkedList<");
Node<E> finger = header;
while (finger != null) {
sb.append(finger.toString());
if (finger.getNext() != null) {
sb.append("-");
}
finger = finger.getNext();
}
sb.append(">");
return sb.toString();
}
}
这是我的Node课程的样子。这里没有太多变化。
public class Node<E> {
private E element;
private Node<E> previous;
private Node<E> next;
public Node<E> getPrevious() {
return previous;
}
public Node<E> getNext() {
return next;
}
public E getElement() {
return element;
}
public Node(E element, Node<E> previous, Node<E> next) {
this.element = element;
this.previous = previous;
this.next = next;
}
@Override
@SuppressWarnings("unchecked")
public boolean equals(Object that) {
if (!(that instanceof Node)) {
return false;
}
Node<E> other = (Node<E>) that;
if (element == null) {
return other.element == null ? true : false;
}
return element.equals(other.element);
}
@Override
public String toString() {
return element.toString();
}
}
这是我用来测试我的实现的代码。
DoublyLinkedList<Integer> dll1 = new DoublyLinkedList<Integer>();
dll1.addFirst(100);
dll1.addFirst(200);
DoublyLinkedList<Integer> dll2 = new DoublyLinkedList<Integer>();
dll2.addFirst(100);
dll2.addFirst(200);
DoublyLinkedList<Integer> dll3 = new DoublyLinkedList<Integer>();
dll3.addFirst(42);
DoublyLinkedList<String> blankList1 = new DoublyLinkedList<String>();
DoublyLinkedList<String> blankList2 = new DoublyLinkedList<String>();
if (blankList1.equals(blankList2)) {
System.out.println(blankList1 + " = " + blankList2);
}
if (!dll1.equals(dll3)) {
System.out.println(dll1 + " != " + dll3);
}
if (dll1.equals(dll2)) {
System.out.println(dll1 + " = " + dll2);
}
输出：
DoublyLinkedList<> = DoublyLinkedList<>
DoublyLinkedList<200-100> != DoublyLinkedList<42>
DoublyLinkedList<200-100> = DoublyLinkedList<200-100>