所以我应该创建一个创建动物列表的程序。该程序按名称对它们进行排序，并按字母顺序将它们放入列表中。但是每次我单击"显示动物"按钮时，它什么也没显示，我发现这是list.size()的问题，所以我将其更改为整数 10 来测试它，它显示但只显示添加的第一个动物。我不确定问题来自哪里，我真的很困惑，这是我的代码：
这是 LinkeList 类
package animal;
import exceptions.ElementNotFoundException;
import exceptions.EmptyCollectionException;
import java.util.*;
/**
* @author Sharon Umute
* Comp 139 001B
* @param <T>
*/
public class LinkedList<T> implements ListADT<T> {
protected int count;
protected SinglyLinkedNode head, tail;
protected int modCount;
/**
* The LinkedList constructor creates an empty list
*/
public LinkedList(){
count=0;
head=tail=null;
modCount = 0;
}
/**
* Removes and returns the head element from this list.
*
* @return the head element from this list
*/
@Override
public T removeFirst() throws EmptyCollectionException {
if(isEmpty()){
throw new EmptyCollectionException("list");
}
T result=(T) head.getElement();
head=head.getNext();
count--;
modCount++;
return result;
}
/**
* Removes and returns the tail element from this list.
*
* @return the tail element from this list
*/
@Override
public T removeLast() throws EmptyCollectionException {
if(isEmpty()){
throw new EmptyCollectionException("list");
}
T result=(T) tail.getElement();
tail=tail.getNext();
count--;
modCount++;
return result;
}
/**
* Removes and returns the specified element from this list.
*
* @param targetElement the target element
* @return the target element
*/
@Override
public T remove(T targetElement) throws EmptyCollectionException, ElementNotFoundException {
if(isEmpty()){
throw new EmptyCollectionException("list");
}
boolean found = false;
SinglyLinkedNode<T> previous = null;
SinglyLinkedNode<T> current = head;
while (current != null && !found)
if (targetElement.equals(current.getElement()))
found = true;
else
{
previous = current;
current = current.getNext();
}
if (!found)
throw new ElementNotFoundException("LinkedList");
if (size() == 1) // only one element in the list
head = tail = null;
else if (current.equals(head)) // target is at the head
head = current.getNext();
else if (current.equals(tail)) // target is at the tail
{
tail = previous;
tail.setNext(null);
}
else // target is in the middle
previous.setNext(current.getNext());
count--;
modCount++;
return current.getElement();
}
/**
* Returns a reference to the head element in this list.
*
* @return a reference to the head element in this list
*/
@Override
public T first() throws EmptyCollectionException {
if(isEmpty()){
throw new EmptyCollectionException("list");
}
T result=(T) head.getElement();
return result;
}
/**
* Returns a reference to the tail element in this list.
*
* @return a reference to the tail element in this list
*/
@Override
public T last() throws EmptyCollectionException {
if(isEmpty()){
throw new EmptyCollectionException("list");
}
T result=(T) tail.getElement();
return result;
}
/**
* Returns true if this list contains the specified target element.
*
* @param target the target that is being sought in the list
* @return true if the list contains this element
*/
@Override
public boolean contains(T target) throws EmptyCollectionException {
if(isEmpty()){
throw new EmptyCollectionException("list");
}
for(T result:this){
if(result.equals(target)){
return true;
}
}
return false;
}
/**
* Returns true if this list contains no elements.
*
* @return true if this list contains no elements
*/
@Override
public boolean isEmpty() {
return(head==null);
}
/**
* Returns the number of elements in this list.
*
* @return the integer representation of number of elements in this list
*/
@Override
public int size() {
return count;
}
/**
* Returns an iterator for the elements in this list.
*
* @return an iterator over the elements in this list
*/
@Override
public Iterator<T> iterator() {
return new LinkedListIterator();
}
private class LinkedListIterator implements Iterator<T>
{
private int iteratorModCount; // the number of elements in the collection
private SinglyLinkedNode<T> current; // the current position
/**
* Sets up this iterator using the specified items.
*
* @param collection the collection the iterator will move over
* @param size the integer size of the collection
*/
public LinkedListIterator()
{
current = head;
iteratorModCount = modCount;
}
/**
* Returns true if this iterator has at least one more element
* to deliver in the iteration.
*
* @return true if this iterator has at least one more element to deliver
* in the iteration
* @throws ConcurrentModificationException if the collection has changed
* while the iterator is in use
*/
public boolean hasNext() throws ConcurrentModificationException
{
if (iteratorModCount != modCount)
throw new ConcurrentModificationException();
return (current != null);
}
/**
* Returns the next element in the iteration. If there are no
* more elements in this iteration, a NoSuchElementException is
* thrown.
*
* @return the next element in the iteration
* @throws NoSuchElementException if the iterator is empty
*/
public T next() throws ConcurrentModificationException
{
if (!hasNext())
throw new NoSuchElementException();
T result = current.getElement();
current = current.getNext();
return result;
}
/**
* The remove operation is not supported.
*
* @throws UnsupportedOperationException if the remove operation is called
*/
public void remove() throws UnsupportedOperationException
{
throw new UnsupportedOperationException();
}
}
}
这是 LinkedOrderedList 类：
package animal;
/**
* @author Sharon Umute
* Comp 139 001B
* @param <T>
*/
public class LinkedOrderedList<T> extends LinkedList<T> implements OrderedListADT<T>{
/**
* Creates an empty list.
*/
public LinkedOrderedList()
{
super();
}
/**
* Adds the specified element to this list at the proper location
*
* @param element the element to be added to this list
*/
@Override
public void add(T element) {
SinglyLinkedNode<T> node =new SinglyLinkedNode<>(element);
SinglyLinkedNode<T> previous=null;
SinglyLinkedNode<T> current=head;
Animal animal;
Animal animal2;
int result;
if(isEmpty()){
tail = head = node;
}else{
int i=0;
while( i<this.size()){
animal=(Animal) current.getElement();
animal2=(Animal) node.getElement();
result=animal.getName().compareTo(animal2.getName());
if((result==-1)&&(current!=head)&&(current!=tail)){
previous=current;
current=current.getNext();
i++;
}else if((result==1)&&(current!=head)&&(current!=tail)){
previous.setNext(node);
}else if((result==0)&&(current!=head)&&(current!=tail)){
i++;
}
if((current==head)||((size()==1)&&(result==1))){
node.setNext(head);
head=node;
}else if((current==tail)||((size()==1)&&(result==-1))){
tail.setNext(node);
tail=node;
}
}
}
}
}
这是名为 SimpleGUI 的 GUI，除了actionPerformed之外，我不允许在这里更改任何内容 所以这是唯一显示的部分：
@Override
public void actionPerformed(ActionEvent ev) throws NullPointerException {
Object object = ev.getSource();
if (object == addReptileButton) {
try {
useA= new Reptile(namePanel.getText(), weightPanel.getValue(),
agePanel.getValue(),reptileLengthPanel.getValue());
} catch (InvalidNameException | InvalidWeightException ex) {
Logger.getLogger(SimpleGUI.class.getName()).log(Level.SEVERE,
null, ex);
}
try{
list.add(useA);
}catch(EmptyCollectionException|NullPointerException ec){
JOptionPane.showMessageDialog(null, "The List isEmpty",
"Input Error",
JOptionPane.ERROR_MESSAGE);
}
}else if (object == addMammalButton) {
try {
useA= new Mammal(namePanel.getText(), weightPanel.getValue(),
agePanel.getValue(),mammalColorPanel.getText());
} catch (InvalidNameException | InvalidWeightException ex) {
Logger.getLogger(SimpleGUI.class.getName()).log(Level.SEVERE,
null, ex);
}
try{
list.add(useA);
}catch(EmptyCollectionException|NullPointerException ec){
JOptionPane.showMessageDialog(null, "The List is Empty",
"Input Error",
JOptionPane.ERROR_MESSAGE);
}
}else if (object == RemoveFirst) {
try{
Animal current = (Animal) list.removeFirst();
}catch(EmptyCollectionException|NullPointerException ec){
JOptionPane.showMessageDialog(null, "The List is Empty",
"Input Error",
JOptionPane.ERROR_MESSAGE);
}
}else if (object == RemoveLast) {
try{
Animal current = (Animal) list.removeLast();
}catch(EmptyCollectionException|NullPointerException ec){
JOptionPane.showMessageDialog(null, "The list is Empty",
"Input Error",
JOptionPane.ERROR_MESSAGE);
}
} else if (object == displayAnimalsButton) {
verifyArea.setText(" ");
try{
for(int j=0; j<10; j++){
Animal result = (Animal) list.removeFirst();
verifyArea.append(result.toString());
list.add(result);
}
}catch(EmptyCollectionException ex){
verifyArea.append(" ");
}
}
}
有人可以告诉我这里的问题是什么以及如何解决它。我真的很感激。
我不知道
这是否是您问题的原因，但是您显示列表的方式有点疯狂。 如果您的实现大小、添加或删除有任何问题，那么每次尝试显示列表时，您都可以将其丢弃。
更好的方法是使用列表迭代器。
但更一般地说，您需要学习如何在 IDE 中使用调试器。 使用调试器是每个程序员都需要掌握的基本技能。 一个不会调试代码的程序员，对雇主来说基本上是无用的。
你需要学习的另一件事是如何编写单元测试。