我是java的新手，我正在做一个链表的作业。我得到了一个测试类，我只需要在链表类的特定位置插入我的代码。首先，我面临的问题是，我无法打印我的列表，看看我的代码是否正常工作，或者我是否取得了任何进展。测试文件使用"printList(nameOftheList)"，但是不打印列表中的任何元素。我尝试使用System.outprintln(nameOftheList)进行测试，但我得到了我认为是列表的位置，而不是列表上的元素。我在这个程序上工作了几天，现在我理解了链表，但是我的书只涵盖了这么多，我还没有能够应用我在网上找到的任何东西。
如果有人能给我指一下正确的方向，我会非常感激的。
这里是给定的测试器:
测试人员:
public class AddTester
{
public static void main(String[] args)
{
LinkedList names = new LinkedList();
names.addFirst("Tom");
names.addFirst("Harry");
names.addFirst("Dick");
names.add("Romeo");
printList(names);
System.out.println("Expected: Dick Harry Tom Romeo");
....
这是我正在学习的课程:
import java.util.NoSuchElementException;
/**
A circular linked list.
*/
public class LinkedList
{
private Node last;
// Don't add other instance fields
/**
Constructs an empty linked list.
*/
public LinkedList()
{
last = null;
}
/**
Returns the first element in the linked list.
@return the first element in the linked list
*/
public Object getFirst()
{
//. . .
if (last == null)
throw new NoSuchElementException();
return last.data;
}
/**
Removes the first element in the linked list.
@return the removed element
*/
public Object removeFirst()
{
//. . .
if (last == null)
throw new NoSuchElementException();
Object element = last.data;
last = last.next;
return element;
}
/**
Adds an element to the front of the linked list.
@param element the element to add
*/
public void addFirst(Object element)
{
//. . .
Node newNode = new Node();
newNode.data = element;
newNode.next = last;
last = newNode;
}
/**
Adds an element to the end of the linked list.
@param element the element to add
*/
public void add(Object element)
{
//. . .
if (last == null)
{
addFirst(element);
//position = last;
}
else
{
Node newNode = new Node();
newNode.data = element;
newNode.next = last.next;
last.next = newNode;
last = newNode;
}
last = last;
}
/**
Returns an iterator for iterating through this list.
@return an iterator for iterating through this list
*/
public ListIterator listIterator()
{
return new LinkedListIterator();
}
private class Node
{
public Object data;
public Node next;
}
private class LinkedListIterator implements ListIterator
{
private Node position;
private Node previous;
/**
Constructs an iterator that points to the front
of the linked list.
*/
public LinkedListIterator()
{
position = null;
previous = null;
}
/**
Moves the iterator past the next element.
@return the traversed element
*/
public Object next()
{
//. . .
if (!hasNext())
throw new NoSuchElementException();
previous = position; //rmbr for remove
if (position == null)
position = last;
else
position = position.next;
return position.data;
}
/**
Tests if there is an element after the iterator
position.
@return true if there is an element after the iterator
position
*/
public boolean hasNext()
{
//. . .
if (position != null)
return true;
else
return false;
}
/**
Adds an element before the iterator position
and moves the iterator past the inserted element.
@param element the element to add
*/
public void add(Object element)
{
//. . .
if (position == null)
{
addFirst(element);
position = last;
}
}
/**
Removes the last traversed element. This method may
only be called after a call to the next() method.
*/
public void remove()
{
//. . .
if (previous == position)
throw new IllegalStateException();
if (position == last)
{
removeFirst();
}
else
{
previous.next = position.next;
}
position = previous;
}
/**
Sets the last traversed element to a different
value.
@param element the element to set
*/
public void set(Object element)
{
if (position == null)
throw new NoSuchElementException();
position.data = element;
}
}
}
这是迭代器:
public interface ListIterator
{
/**
Moves the iterator past the next element.
@return the traversed element
*/
Object next();
/**
Tests if there is an element after the iterator
position.
@return true if there is an element after the iterator
position
*/
boolean hasNext();
/**
Adds an element before the iterator position
and moves the iterator past the inserted element.
@param element the element to add
*/
void add(Object element);
/**
Removes the last traversed element. This method may
only be called after a call to the next() method.
*/
void remove();
/**
Sets the last traversed element to a different
value.
@param element the element to set
*/
void set(Object element);
}
使用迭代器或您的LinkedList:
static String printList(LinkedList names){
StringBuilder sb = new StringBuilder("Expected : ");
ListIterator st = names.listIterator();
while(st.hasNext()){
//Here implements stuff to get the element of your linkedList and add
//it to the StringBuilder
}
return sb.toString();
}
在LinkedListIterator的构造函数中，您将字段position设置为null，并且(除非我错过了一些东西)这永远不会改变。
然后，在hasNext()中，检查position == null是否存在，如果存在则返回false。
这意味着，如果printList正在使用您的LinkedListIterator，它可能正在检查hasNext()以确定何时停止打印。由于您的hasNext()总是返回false，因此printList只能假设它正在查看空列表。